TH  E  WAYS 


OF 


THE  PLANETS 


MARTHA  EVANS  MARTIN 


GIFT  OF 
BOHEMIAN  CLUB 


X? 


A  WHIRLING  SPIRAL   NEBULA,   TYPICAL   OF  THAT  FROM   WHICH  THE  SUN 
AND    PLANETS    WERE    PROBABLY    EVOLVED 

In  the  process  of  evolution  the  dense  center  becomes  the  controlling  sun  and  the 
smaller  spots  of  condensation  form  the  planets.  This  particular  nebula  lies  just 
under  the  end  of  the  handle  of  the  Big  Dipper.  It  was  photographed  at  Mt.  Wilson 
Observatory. 


I 


THE  WAYS  OF 

THE  PLANETS 


BY 

MARTHA  EVANS  MARTIN,  A.M. 

AUTHOR  OF    l\ 

"THE  FRIENDLY  STARS" 


: 


NEW  YORK  AND   LONDON 

HARPER  5-  BROTHERS  PUBLISHERS 

MCMXII 


Astron.  Dept. 


ASTRONOMY  DEPT 


COPYRIGHT.    1912.    BY   HARPER   a    BROTHERS 

PRINTED   IN   THE   UNITED   STATES   OF  AMERICA 

PUBLISHED   OCTOBER,    1912 


K-M 


CONTENTS 

CHAP.  PAGE 

I.  ON    MAKING    ACQUAINTANCE    WITH    THE 

PLANETS     i 

II.  OUR  RELATION  TO  THE  PLANETS  .-•  .    .    .      n 

III.  WHAT  THE  PLANETS  ARE,  AND  WHAT  THEY 

APPEAR  TO  BE 17 

IV.  THE  ORIGIN  OF  THE  PLANETS 26 

V.  THE  SEVEN  GREAT  PLANETS 38 

VI.  THE  MOVEMENTS  OF  THE  PLANETS    ...  46 

VII.  How  THE  INFERIOR  PLANETS  SEEM  TO  MOVE  56 

VIII.  How  THE  SUPERIOR  PLANETS  SEEM  TO  MOVE  65 

IX.  THE  PATH  OF  THE  PLANETS 71 

X.  MERCURY — WHEN    AND  WHERE    TO  FIND 

MERCURY — DISTANCE  AND  BRIGHTNESS 
— MERCURY'S  SIZE  AND  THE  CONSE- 
QUENCES OF  IT — WHAT  THE  SUN  DOES 
FOR  MERCURY — TRANSITS 93 

XI.  VENUS — WHEN  AND  WHERE  TO  SEE  VENUS — 

DISTANCE  AND  BRILLIANCY — VENUS'S 
LIKENESS  TO  THE  EARTH — ATMOSPHERE, 
DAY  AND  NIGHT,  AND  SEASONS — TRAN- 
SITS .  122 


701044 


CONTENTS 

CHAP.  PAGE 

XII.  MARS— How  TO  IDENTIFY  MARS— WHEN  AND 

WHERE  MARS  MAY  BE  SEEN — SIZE, 
ATMOSPHERE,  AND  TEMPERATURE — DIS- 
TANCE AND  BRILLIANCY  —  DAY  AND 
NIGHT,  AND  SEASONS — SURFACE  ASPECTS 
— SATELLITES 151 

XIII.  JUPITER— PLACE    IN    THE    SKY — DISTANCE, 

LIGHT,  AND  HEAT — DAY  AND  NIGHT, 
SEASONS,  AND  ATMOSPHERE — SURFACE 
FEATURES — SYSTEM  OF  SATELLITES  .  .  183 

XIV.  SATURN— AROUND    ONE    CIRCUIT    OF    THE 

SKIES  WITH  SATURN — DISTANCE  AND  SIZE 
— SURFACE  ASPECTS  AND  CONSTITUTION 
— DAY  AND  NIGHT  —  THE  RINGS  AND 

MOONS  OF  SATURN — SEASONS  ....  206 

XV.  URANUS 225 

XVI.  NEPTUNE 234 

XVII.  THE  LITTLE  PLANETS,  OR  THE  ASTEROIDS  .  244 

XVIII.  CONCLUSION 258 

SYMBOLS  USED  IN  ALMANACS 267 

INDEX 269 


ILLUSTRATIONS 

A  WHIRLING  SPIRAL  NEBULA,  TYPICAL  OF  THAT 
FROM  WHICH  THE  SUN  AND  PLANETS  WERE 
PROBABLY  EVOLVED Frontispiece 

MAP  SHOWING  THE  CONSTELLATIONS  OF  THE 
ZODIAC  AND  THE  LINE  OF  THE  ECLIPTIC  RUN- 
NING THROUGH  THEM  Facing  p.  76 

THE  LOVELY  CRESCENT  THAT  VENUS  SHOWS 
WHEN  TO  OUR  VIEW  SHE  IS  AT  HER  GREATEST 
BRILLIANCY 13^ 

RELATIVE  APPARENT  SIZE  OF  VENUS  AT  DIF- 
FERENT PHASES  OF  ILLUMINATION  .  .  .  Page  137 

THE   TWO   PHASES   OF   MARS Facing  p.  I$2 

MARS:  DIFFERENCE  IN  ITS  APPARENT  SIZE  AT 

ITS  NEAREST,  MIDDLE,  AND  FARTHEST  DIS- 
TANCE FROM  THE  EARTH Page  169 

JUPITER,  THE  MAMMOTH  MEMBER  OF  THE  SOLAR 
FAMILY— LARGER  THAN  ALL  THE  OTHER 
PLANETS  PUT  TOGETHER Facing  p.  184 

SATURN   AND   ITS   RINGS "         22O 


THE 
WAYS  OF  THE  PLANETS 


ON  MAKING  ACQUAINTANCE  WITH  THE  PLANETS 

IT  is  sought  in  the  following  pages  to  give 
a  simple  account  of  what  may  now  be  said 
to  be  known  of  the  character  of  the  planets, 
and  to  describe  with  as  little  technicality  as 
possible  their  movements  and  aspects  and  re- 
lations. An  endeavor  is  made  to  impart  con- 
cerning each  one  of  them  not,  surely,  pro- 
found learning,  but  just  a  good,  every-day, 
practical  notion,  so  that  the  mere  name  will 
call  up  a  definite  object,  with  its  own  attri- 
butes, appearance,  and  behavior,  entirely 
distinct  from  any  other  planet  or  from  any 
other  object  in  the  skies. 
An  endeavor  is  made  also  to  so  simplify 


>   .  IHE.WAYS    OF    THE    PLANETS 


and  direct  the  observation  that  any  one,  after 
a  little  practice,  will  know  almost  without 
hesitation,  on  seeing  a  planet  in  the  sky,  that 
it  is  a  planet,  and  not  a  fixed  star,  and  exactly 
what  planet  it  is.  The  situation  and  aspect 
of  it  will  then  as  quickly  and  clearly  pro- 
nounce it  to  be  the  individual  planet  that  it 
is  as  the  sight  of  a  person  of  one's  acquaint- 
ance proclaims  him  to  be  that  person,  and  no 
other.  The  very  name  of  Venus,  for  example, 
and  still  more  the  sight  of  Venus,  will  call 
up  a  conception  of  Venus,  with  the  particular 
atmosphere  and  light  and  movements  and 
wanderings  which  make  her  what  she  is.  On 
looking  at  her  the  observer  will  at  once  know 
why  she  occupies  the  special  position  in  the 
sky  in  which  he  sees  her,  why  she  is  not  so 
bright  as  she  was  when  she  was  last  in  view, 
or  is  so  much  brighter  than  she  was  then, 
about  how  long  she  is  likely  to  remain  where 
she  is,  and  when  she  goes  what  will  become 
of  her. 

For  far  off  and  truly  mysterious  as  the 
planets  are,  it  still  is  with  them  as  with  most 
other  objects  in  nature:  a  very  little  knowl- 
edge of  their  aspects  and  their  ways  begets 
a  sense  about  them  that  makes  the  most 
casual  observation  of  them  interesting  and, 


ACQUAINTANCE  WITH   THE    PLANETS 

as  far  as  it  goes,  intelligent.  The  slightest 
glance  at  them  betrays  some  shape,  or  posi- 
tion, or  light,  or  other  quality,  which  at  once 
makes  recognition  of  them  unmistakable. 
They  disclose  themselves  oftentimes,  one  can 
scarcely  say  how,  just  as  persons  with  whom 
we  are  intimate  do  by  some  half-caught 
outline,  motion,  or  posture;  or  just  as  the 
trees  do  to  an  observer  who  knows,  for  ex- 
ample, an  oak-tree  from  an  elm,  whether  they 
are  covered  with  their  own  peculiar  verdure, 
or  whether  they  stand  with  bare  branches 
stretched  out  and  colored  in  their  own 
peculiar  way. 

This  instant  recognition  of  the  planets  is, 
of  course,  not  to  be  had  by  simply  reading 
about  them.  Such  practical  familiarity  with 
them  is  attained  only  by  seeking  them  out 
over  and  over  again  and  looking  at  them  with 
attention,  with  eagerness,  and  with  all  one's 
faculty.  With  them,  as  with  other  natural 
objects,  it  requires  observation  truly  to  know 
them.  But  then,  observation,  when  one  gets 
a  little  started  in  it,  is  a  great  deal  more 
interesting,  a  great  deal  more  absorbing,  than 
any  reading  about  them  can  ever  be.  It  is 
also  a  very  easy  thing  to  begin,  for,  after  all, 
it  is  not  much  more  than  looking  and  then 
2  3 


THE    WAYS    OF    THE    PLANETS 

looking  again.  In  doing  this  one  can  hard- 
ly tell  just  when  an  object  ceases  to  be 
strange,  and  then  becomes  familiar,  and 
finally  is  so  much  a  part  of  every-day  knowl- 
edge that  one  knows  it  at  a  glance.  But 
this  is  what  happens  in  the  case  of  any 
natural  object  when  we  observe  it  often  and 
with  true  attention. 

In  the  case  of  the  planets,  if  one  is  inter- 
ested at  all,  every  stage  in  the  cultivation 
of  such  an  acquaintance  is  full  of  pleasure. 
Even  to  one  who  regards  them  only  as  a 
part  of  the  general  aspect  of  the  sky,  they 
are  the  most  beautiful  objects  in  it  and 
always  the  first  to  attract  special  attention. 
Nine  times  out  of  ten,  when  any  one  asks 
what  a  certain  star  is,  it  proves  to  be  one 
of  the  planets.  When  one  of  them  is  visible 
a  person  can  hardly  glance  at  the  heavens 
without  noticing  it,  even  if  he  does  not  stop 
to  think  about  it.  But  if  he  does  stop  to 
think  about  it  and  notices  that  it  is  far 
larger  than  any  star  he  has  noted  before, 
that  it  hangs  low  in  the  western  sky  early 
in  the  evening,  and  shines  with  a  brilliant 
silvery  light,  and  if  he  then  learns  that  it 
is  Venus,  will  he  not  always  have  a  pleasant 
thrill  of  recognition  when  he  again  sees  such 
4 


ACQUAINTANCE  WITH   THE   PLANETS 

a  star  in  such  a  position  and  knows  it  as 
Venus,  among  the  planets  as  surpassing  in 
beauty  as  the  goddess  of  that  name  was 
among  the  immortals?  Or,  if  in  the  east, 
at  the  same  time  in  the  evening,  he  sees  a 
brilliant,  solid-looking,  unblinking  star  shin- 
ing with  a  white  light,  but  pinkish  white,  not 
silvery,  and  finds  it  to  be  Jupiter,  will  not  such 
a  star  in  such  a  situation  be  to  him  ever 
after  a  pleasant  acquaintance  that  he  can 
call  by  name?  Not  that  Jupiter  and  Venus 
are  always  in  these  positions,  or  shine  in 
just  this  way  at  all  times.  These  are  their 
places  and  aspects  at  certain  times,  fre- 
quently recurring,  and  at  such  times  always 
unmistakably  distinguish  them. 

It  is,  then,  merely  the  matter  of  a  little 
more  and  yet  a  little  more  observation,  in 
order  to  come  to  know  any  one  of  the  vis- 
ible planets  in  all  its  varying  aspects  and 
situations.  Of  course,  at  the  start  some  guid- 
ance is  necessary,  but  only  a  little;  and  that 
little,  if  it  is  of  the  right  sort,  should  not  be 
irksome.  To  provide  such  guidance  is  one 
of  the  aims  of  this  book.  That  is,  indeed, 
its  main  aim. 

But  in  addition  to  what,  as  a  help  in  ob- 
servation, it  may  find  to  say  regarding  the 
5 


THE    WAYS    OF    THE    PLANETS 

appearance  and  movements  of  the  planets, 
it  will  endeavor  to  give  also  ample  informa- 
tion concerning  their  character  and  con- 
stitution. 

It  is  hoped  that  this  may  be  done  without 
weighting  the  narrative  with  figures,  though 
some  of  the  peculiarities  of  the  planets  must 
be  expressed  by  means  of  numbers.  Cer- 
tainly no  mathematical  problems  will  be 
presented.  But  it  will  be  profitable  to 
remember  that  every  one  of  the  intimate 
things  we  know  about  the  planets  has  come 
to  us  through  the  long  and  laborious  mathe- 
matical work  of  astronomers.  To  them  we 
owe  the  extinguishable  debt  that  we  owe  to 
all  special  workers  who  put  us  in  possession 
of  the  facts  that  interpret  life  to  us. 

For  the  astrology  and  poetry  and  romance 
of  the  planets  one  must  go  elsewhere. 
Nearly  every  book  on  the  subject  of  the 
planets — and  there  are  many  of  them — has 
some  information  about  these  things;  and 
properly,  too,  for  every  genuine  emotion 
and  every  real  fancy  has  its  value.  But 
neither  curious  lore  of  the  planets  nor  the 
sentiment  and  emotion  they  have  produced 
in  others  is  what  the  author  of  this  book 
is  striving  to  set  forth.  It  is  something  much 
6 


ACQUAINTANCE  WITH  THE   PLANETS 

more  vital  than  this.  What  we  wish  to 
contemplate  here  are  the  plain  facts,  the 
knowledge  of  which  enlivens  and  enriches 
one's  mind  and  nature.  If  the  contempla- 
tion of  them  kindles  one's  fancy  or  excites 
one's  emotions,  these  results  at  least  will 
not  be  second-hand.  If  the  bare  facts, 
simply  and  plainly  told,  and  the  view  of 
the  planets  themselves  as  they  wander 
through  their  courses  in  the  sky,  do  not 
awaken  one's  understanding  and  imagina- 
tion, no  amount  of  poetry  or  romance  that 
other  people  have  built  up  around  the 
planets  will  arouse  anything  more  than  a 
factitious  interest  in  them.  It  is  when  our 
own  faculties  are  at  work  and  our  own  fancy 
plays  over  a  subject  that  we  become  genuine- 
ly and  lastingly  interested  in  it. 

The  facts  themselves  are  in  the  main  quite 
simple,  and  will  not  be  given  here  as  any- 
thing else  than  that.  They  have  been  fair- 
ly wrested  from  that  mysterious  thing  called 
space  by  the  mighty  power  of  mind  and  un- 
ceasing labor.  Our  knowledge  of  them  is 
due  to  long  nights  of  watching  and  long 
days  of  calculating;  to  long  and  careful 
testing  and  considering  of  theories,  only  to 
find  that  something  else  must  be  tried;  to 
7 


THE    WAYS    OF    THE    PLANETS 

courage  to  begin  all  over  again,  to  sudden 
inspirations,  and  sometimes  to  those  lucky 
discoveries  that  seem  almost  like  miracles. 

The  subject  of  the  planets  has  in  some  re- 
spects a  greater  interest  even  than  that  of 
the  stars,  because  we  know,  after  all,  more 
about  them.  We  sometimes  have  a  feeling, 
though,  that  we  know  more  of  the  stars,  al- 
though the  stars  are  so  much  farther  off. 
Why  we  have  this  feeling  it  is  easy  to  explain. 
Knowing  them  to  be  so  far  removed  from  us, 
we  really  approach  the  stars  with  a  different 
expectation.  The  few  things  that  we  have 
learned  about  them  have  in  themselves  such 
a  magnitude  that  it  makes  them  seem  a 
greater  body  of  knowledge  than  they  truly 
are.  The  stars  are  indeed  so  far  away,  and 
what  we  know  of  them  has  to  be  expressed 
in  such  large  terms,  that  the  mind  does  not 
demand  in  that  information  the  minute  ex- 
actness that  it  seeks  for  in  the  case  of  nearer 
objects. 

In  the  case  of  the  stars,  we  seek  mainly  to 
know  their  distances,  the  direction  of  their 
motions,  the  speed  with  which  they  travel, 
and  their  probable  connection  with  each 
other.  The  fact  that  in  computing  the  dis- 
tance of  a  single  star,  many  trillions  of  miles 
8 


ACQUAINTANCE   WITH   THE   PLANETS 

away,  the  result  may  be  a  little  less  than 
exact  does  not  keep  us  from  learning  what 
ones  are  sufficiently  near  for  their  distances 
to  be  measured  at  all  and  what  ones  are  im- 
measurably remote.  Whether  they  travel  at 
the  rate  of  exactly  three  or  three  hundred 
miles  a  second,  we  can  learn  that  some  are 
traveling  at  somewhat  the  same  rate  of  speed 
as  our  sun  travels,  and  some  incredibly  faster; 
that  certain  groups  are  going  in  one  direction 
and  certain  groups  in  another;  that  some  are 
approaching  us  and  some  are  receding  from 
us.  And  thus  we  can  classify  them  and  learn 
the  significance  of  these  facts,  and,  little  by 
little,  gain  a  definite  understanding  of  the 
construction  and  meaning  of  the  entire  uni- 
verse. Their  very  remoteness  gives  a  cer- 
tain compactness  to  the  information  we  have 
about  the  stars,  by  making  it  necessary  to 
generalize  more  than  we  would  if  they  were 
near  enough  to  yield  more  details;  and  we 
are  in  a  way  satisfied  with  this  more  general 
sort  of  knowledge  of  them. 

But  the  very  fact  of  our  knowing  so  much 
about  the  planets  extends  our  curiosity  con- 
cerning them  and  makes  us  feel  that  we  ought 
to  know  more.  The  mind  is  provoked  into 
more  minute  speculations  about  them,  and 
9 


THE    WAYS    OF    THE    PLANETS 

we  demand  more  exactness  of  information 
and  knowledge  of  a  more  specific  or  intimate 
sort  than  would  satisfy  us  in  regard  to  the 
stars.  Atmosphere,  habitability,  exact  size, 
seasons,  and  day  and  night,  are  the  kind  of 
things  we  most  seek  to  know  in  reference  to 
the  planets.  These  are  such  definite  things 
that  conclusions  concerning  them  are  subject 
to  close  criticism,  and  differences  of  opin- 
ion in  regard  to  them  thus  sometimes  occur 
which  tend  to  give  one  a  more  or  less  con- 
fused notion  of  what  is  really  known.  As  a 
matter  of  fact,  our  information  about  the 
planets  is  much  fuller  than  our  knowledge 
of  the  stars,  as  we  would  naturally  expect  it 
to  be.  Much  of  what  we  seek  to  know  about 
the  stars  has  long  been  common  knowledge 
about  the  planets. 


II 

OUR  RELATION  TO  THE  PLANETS 

TO  know  about  the  planets  is  to  know 
about  ourselves.  The  earth  is  one  of 
them.  Whatever  their  origin,  the  earth's  is 
the  same.  It  and  they  are  formed  from  the 
same  nebula,  controlled  by  the  same  central 
body,  subject  to  the  same  laws,  and  destined 
for  the  same  fate  in  the  end.  In  this,  the 
stars  and  the  planets  are  not  alike.  They  all 
shine  upon  us  with  the  same  sweet  friendli- 
ness, and  commonly  we  make  no  difference 
between  them  in  our  feeling  for  them.  But 
the  stars  are  bright  and  beautiful  acquaint- 
ances living  far  away  in  their  own  domain. 
The  planets  are  members  of  our  own  family, 
bone  of  our  bone  and  flesh  of  our  flesh,  living 
comparatively  near  to  us,  within  the  domain 
of  our  common  source  of  life,  the  sun. 

One  evening  last  autumn  I  was  coming 
up  Broadway,  New  York,  with  a  friend,  when 
we  encountered  at  Union  Square  a  man  with 
il 


THE    WAYS    OF    THE    PLANETS 

a  six-inch  telescope  directed  toward  the  east- 
ern sky.  He  was  soliciting  those  who  passed 
to  stop  and  look  at  Mars  and  Saturn.  Both 
of  these  planets  were  then  very  bright. 
They  were  also  fairly  near  together,  and  so 
low  in  the  east  that  one  could  scarcely  help 
seeing  them.  But  the  people  passed  back 
and  forth  with  hardly  so  much  as  a  glance  at 
the  man  and  his  telescope,  and  for  the  most 
part  never  even  raised  their  eyes  to  the  sky 
with  a  passing  curiosity  to  see.  what  it  might 
be  that  he  wanted  to  show  them.  My  friend 
and  I  stopped  and  took  each  a  view  first  of 
Mars  and  then  of  Saturn.  While  we  were 
looking  at  the  planets,  a  few  of  the  passers-by 
began  to  loiter  about,  half  smiling  at  us  for 
so  playing  in  public,  slightly  curious  to  see 
how  we  were  faring  at  it,  but  for  the  most 
part  apparently  indifferent  to  what  we  were 
seeing.  We  had  a  fine  view  of  Saturn  lightly 
resting  in  his  nest  of  rings,  and  an  equally 
good  view  of  the  comical  "eye"  of  Mars. 

After  we  had  finished,  one  or  two  others, 
evidently  prompted  by  our  example,  fol- 
lowed us  at  the  telescope.  One  or  two  in- 
quired of  us  what  the  stars  were  that  had 
so  interested  us,  and  one,  pointing  to  Mars, 
wanted  to  know  if  it  was  Venus.  As  the 


OUR    RELATION    TO    THE    PLANETS 

crowd  grew  larger  a  few  more  ventured  to 
take  a  look,  much  as  they  might  venture 
to  take  their  chance  at  hitting  the  bull's- 
eye  in  some  shooting-gallery.  With  the 
telescope  pointed  at  Saturn,  the  man  dron- 
ingly chanted:  "This  planet  is  887,000,000 
miles  from  the  sun.  The  ring  you  see  is 
170,000  miles  in  diameter,"  and  so  on. 
These,  to  be  sure,  were'  the  facts — and  most 
marvelous  facts,  too — but  without  much 
meaning  to  one  who  knows  nothing  much 
about  the  planets;  and  the  manner  of  their 
recital  certainly  did  not  make  them  allur- 
ing. I  could  not  myself  help  feeling  that 
the  people  there  were  missing  a  valuable 
opportunity,  and  that  it  would  be  only  fair 
to  them  for  some  one  fairly  to  cry  out: 
"Come  here  and  look  at  this  planet.  It  is 
different  from  anything  else  you  have  ever 
seen  or  ever  will  see.  It  was  at  one  time 
a  part  of  the  same  nebulous  mass  that  we 
were  a  part  of.  It  is  in  the  same  system  of 
worlds  with  us.  It  was  formed  in  the  same 
way  that  this  world  was  formed.  It  is  in 
itself  the  most  wonderful  thing  you  ever 
saw,  and  it  is  bound,  as  we  are,  to  the  sun 
by  the  ever-drawing  tie  of  gravitation.  The 
very  position  of  our  own  world  in  space  is 
13 


THE    WAYS    OF    THE    PLANETS 

/more  or  less  influenced  by  it.     If  anything 
^  should  happen  to  it,  it  might  be  a  serious 
matter  to  us." 

For  it  is  true  that  we  are  thus  closely 
bound  to  the  planets.  The  family  tie  among 
us  is  of  far  more  force  and  significance  than 
in  any  ordinary  case  of  common  origin. 
Human  family  ties  wear,  as  we  know,  often 
into  the  merest  threads,  or  even  become  no 
ties  at  all.  But  that  between  the  earth  and 
the  planets  remains  apparently  as  close  and 
strong  as  ever  it  was.  The  law  of  gravity, 
under  which  the  earth  draws  toward  its  cen- 
ter every  atom  of  matter  surrounding  it,  and 
thus  holds  together  all  the  atoms  composing 
it,  is  not  solely  terrestrial  in  its  application. 
It  is  probably  universal.  It  certainly  ap- 
plies to  every  part  of  our  little  family  of 
,  .worlds.  Every  particle  in  the  solar  system 
attracts  toward  it  every  other  particle  in 
that  system  with  a  force  determined  by  its 
mass  and  its  distance.  The  sun,  by  reason 
of  its  immense  size,  compels  the  earth  and  all 
the  other  planets  forever  to  circle  around  it. 
But  the  planets  themselves  have  just  as  much 
power  of  attraction  as  the  sun,  atom  for  atom. 
Thus,  while  the  sun  controls  the  motions 
of  all  of  them,  each  pulls  at  the  other,  and, 
14 


OUR    RELATION    TO    THE    PLANETS 

according  to  its  power,  determines  how  much 
the  path  of  each  shall  vary  from  the  course 
around  the  sun  it  otherwise  would  make. 
In  the  case  of  the  smaller  planets,  this 
gravitational  influence  is,  of  course,  very  slight, 
and  so  subtle  that  we  here  on  earth  are  not 
even  conscious  of  it.  But  it  is,  nevertheless, 
real  and  continuous.  It  is  greatest  between 
the  two  largest  planets,  Jupiter  and  Saturn; 
but  it  was  enough  in  the  case  of  Uranus  and 
Neptune  to  lead,  by  its  mere  manifestation 
on  the  earth,  to  the  discovery  of  Neptune, 
the  farthest  planet. 

Being  thus  of  the  same  origin  with  the 
planets,  having  the  same  life  history,  being 
bound  to  them  in  space  by  a  tie  that  is  per- 
haps eternal,  how  can  we  fail  to  have  the 
most  intimate  interest  in  their  nature  and 
all  that  concerns  them? 

But  in  addition  to  their  close  relationship 
to  us  there  is,  to  make  them  of  peculiar 
interest,  the  fact  that,  after  the  sun  and  the 
moon,  they  are  for  our  eyes  the  most  splen- 
did objects  in  all  the  brilliant  panorama  of 
the  sky.  Such  of  them  as  we  can  see  at 
all  with  the  naked  eye  are  most  of  the  time 
much  brighter  than  any  first -magnitude 
star.  As  they  wander  from  constellation  to 
15 


THE    WAYS    OF    THE    PLANETS 

constellation  the  soft  light  of  their  placid  faces 
gives  a  beauty  and  variety  to  the  spectacle 
that  endears  them  to  us,  and  at  the  same 
time  enhances  by  contrast  their  own  charm 
and  that  of  the  glittering,  unchanging  stars. 
There  is  nothing  that  gives  one  such  a 
sense  of  sweet  familiarity  with  the  heavens 
as  a  really  recognizing  acquaintance  with 
the  planets.  They  are  not,  like  the  stars, 
^aTssociated  with  particular  seasons.  They 
come  sometimes  with  the  gay  company  of 
stars  that  dance  their  way  across  the  cold 
winter  skies,  and  sometimes  with  those  that 
shine  during  the  soft  summer  nights.  Often 
in  the  spring  and  autumn  we  see  some  one 
of  them  before  the  sun  is  fairly  down,  and, 
before  the  light  of  an  ordinary  star  can  yet 
be  seen,  hanging  in  lone  brilliancy  as  the 
evening  star;  and  often  an  early  riser  has 
the  reward  of  seeing  one  as  a  morning  star 
glowing  almost  in  the  rays  of  the  rising  sun. 
Thus  they  are,  one  and  another,  with  us  at 
all  times  and  seasons,  and  it  accords  with  the 
fact  of  the  relation  being  a  family  one  that 
we  have  in  their  coming  and  going  a  sense 
of  frequency  and  informality  which  we  can- 
not have  in  the  more  regular  and  seasonal 
coming  and  going  of  the  stars. 


Ill 

WHAT  THE  PLANETS  ARE,  AND  WHAT 
THEY  APPEAR  TO  BE 

THE  planets  are  dark,  opaque  bodies 
which  revolve  at  varying  distances  and 
at  varying  rates  of  speed  in  orbits  more  or 
less  circular  around  the  sun  as  a  center. 
They  have  no  light  of  their  own,  as  the 
stars  have,  but  shine  wholly  by  reflected 
light  received,  from  the  sun,  which  itself  is 
a  star.  The  amount  of  light  they  show  to 
us  depends  upon  their  size,  their  distance, 
and  their  power  of  reflecting  the  light  they 
receive. 

In  comparison  with  the  stars,  the  planets 
are  very  near  to  us.  Our  sun,  which  is  in 
constitution  a  star,  but  very  widely  sepa- 
rated from  any  other  star  in  the  universe, 
holds  all  his  family  of  planets  by  the  tether 
of  gravitation,  and  so  keeps  them  circling 
about  him  in  a  very  small  space,  as  astronom- 
17 


THE    WAYS    OF    THE    PLANETS 

ical  space  is  measured.  To  all  of  the  planets 
except  Mercury,  we  ourselves  are  nearer 
than  the  sun  is.  To  be  sure,  this  distance 
between  us  and  the  planets,  as  measured 
by  any  terrestrial  measure,  is  not  exactly 
small.  It  is  only  by  comparison  that  we 
can  be  said  to  have  anything  like  a  cozy 
relation  to  them.  For  merely  earthly  affairs 
we  use  terrestrial  measures.  In  solar  affairs 
we  measure  by  an  astronomical  unit,  which 
is  the  sun's  distance  from  the  earth,  ninety- 
three  millions  of  miles.  When  we  say  a 
planet's  distance  from  the  sun  is  thirty 
astronomical  units,  we  mean  it  is  thirty 

X/times  farther  than  the  earth  is  from  the 
sun. 

For  matters  outside  of  the  solar  system, 
the  unit  of  measure  is  the  number  of  miles 
that  light  travels  in  a  year.  The  speed  of 
light  is  a  little  more  than  186,000  miles  in 
a  second.  This  is  equal  to  about  six  trillions 
of  miles  in  a  year,  or  about  sixty-three 
thousand  times  the  distance  of  the  sun 
from  the  earth,  our  family  measuring-stick. 
From  the  nearest  star  it  takes  light  more 
than  four  years  to  come  to  us.  From  the 

vx  nearest    planet    light   comes    in    less    than 
three  minutes,  and  from  the  farthest  one  it 
18 


WHAT    THE    PLANETS    ARE 

makes  the  journey  in  a  little  more  than  four 
hours. 

As  compared  with  other  heavenly  bodies, 
therefore,  the  sun  and  the  planets  are  very 
near  together,  occupying  a  very  small  space 
in  the  immensity  of  the  universe,  immeasur- 
ably isolated  from  all  the  other  systems  and, 
so  far  as  we  know,  immeasurably  smaller  as 
a  system  than  most  of  them. 

The  whole  body  of  the  planets  is  divided 
according  to  size  into  two  classes,  the  major 
and  the  minor  planets.  When  we  refer 
generally  to  the  planets,  the  major  planets 
only  are  meant.  The  minor  planets  are 
usually  called  the  asteroids,  or  planetoids. 
There  are  many  hundreds  of  them,  and  only 
one — and  that  barely — can  be  seen  with  the 
naked  eye.  The  other  planets  are  eight  in 
number,  including  the  earth,  which  is,  after 
all,  nothing  but  one  of  the  smaller  of  the 
major  planets.  They  are,  in  the  order  of 
their  distances  from  the  sun:  Mercury,  the 
nearest,  Venus,  the  Earth,  Mars,  Jupiter, 
Saturn,  Uranus,  and  Neptune.  Of  these 
only  five — Mercury,  Venus,  Mars,  Jupiter, 
and  Saturn — can  be  seen  from  the  earth  with- 
out optical  aid.  Occasionally,  when  Uranus 
is  very  favorably  situated,  a  person  with  an 

3  19 


THE    WAYS    OF    THE    PLANETS 

exceptionally  good  eye,  who  knows  exactly 
where  to  look  for  the  planet,  can  see  it. 
Neptune  is  about  equal  to  an  eighth-magni- 
tude star  in  brightness,  and  can  never  be 
seen  without  the  aid  of  a  telescope.  Mer- 
cury, while  quite  bright  enough  to  be  seen, 
is  not  often  situated  favorably  for  observa- 
tion. It  is  very  near  the  sun,  and  is  gener- 
ally obscured  either  by  the  light  of  the  sun 
when  the  sun  and  the  planet  are  above  the 
horizon,  or  by  the  haziness  of  the  atmos- 
phere when  the  sun  is  below  the  horizon 
and  the  planet  a  little  above  it.  In  regions 
of  considerable  altitude  with  a  clear,  rare 
atmosphere,  Mercury  is  more  often  seen; 
but  never  for  very  long  at  a  time. 

The  only  planets,  therefore,  that  are  a 
art  of  our  evening  spectacle  in  the  skies 
are  Venus,  Mars,  Jupiter,  and  Saturn. 
These  four  happen  to  be  not  only  the  ones 
we  oftenest  see,  but  also  the  most  interest- 
ing of  all  the  planets  from  various  points 
of  view.  Venus  and  Mars  are  the  nearest 
to  the  earth,  and  most  resemble  it,  and  hence 
are  the  most  inviting  for  speculations  which 
have  a  human  interest,  such  as  habit  abil- 
ity, the  presence  of  life,  and  kindred  ideas. 
Jupiter  and  Saturn  are  interesting  above  all 
20 


WHAT    THE    PLANETS    ARE 

the  others  in  their  splendor  and  size,  and 
in  their  importance  as  the  centers  of  systems 
of  their  own. 

As  seen  by  us,  the  planets  are  similar  to 
the  stars,  but  with  very  distinct  differences 
in  appearance,  which,  when  once  familiar, 
mark  them  so  unmistakably  as  planets,  and 
not  fixed  stars,  that  we  need  never  get  the 
two  confused.  The  first  and  easiest  dis- 
tinguishing mark  to  notice  is  that  they  do 
not  twinkle,  as  the  stars  do,  but  shine  with 
a  steady  light  similar  to  that  of  the  moon. 
This  is  an  invariable  difference  between 
stars  and  planets,  and  one  needs  only  to 
stop  and  truly  look  at  them  in  order  to  de- 
tect it.  And  once  it  has  become  familiar, 
it  discloses  itself  at  a  glance. 

This  difference  between  stars  and  planets 
is  due  almost  solely  to  difference  of  distance, 
though  the  twinkling  is  caused  by  our  own 
atmosphere.  The  stars  are  too  far  away 
to  send  us  anything  but  a  mere  point  of 
light,  and  the  unequal  density  of  the  waves 
of  air  sweeping  over  this  point  of  light  keeps 
it  dancing  before  our  eyes,  causing  the 
phenomenon  that  we  call  twinkling.  But 
the  planets,  being  nearer  to  us,  show  a  disc, 
from  every  point  of  which  comes  a  line  of 

21 


THE    WAYS    OF    THE    PLANETS 

light,  making  the  total  light  of  some  volume; 
and  these  inequalities  of  the  air  are  too  small 
to  interfere  with  it  to  any  extent.  Some- 
times, when  the  atmosphere  is  particularly 
unsteady,  it  happens  that  the  light  of  a 
planet  is  somewhat  affected  by  it  when  the 
planet  is  just  rising  or  setting  and  is,  con- 
sequently, near  the  horizon,  and  that  it  then 
seems  to  twinkle  a  little.  But  this  depart- 
ure from  the  rule  is  always  slight  and  of 
short  duration,  in  the  case  of  the  four 
planets  most  seen.  Mercury,  never  being 
seen  anywhere  except  near  the  horizon, 
often  seems  to  twinkle;  but  then  he  is  sel- 
dom seen  at  all,  and,  when  visible,  is  in  other 
ways  so  well  marked  that  one  cannot  fail 
to  recognize  him. 

So  the  steady  light  may  justly  be  said  to 
be  invariable,  because  the  unusual  condi- 
tions are  easily  detected.  When  the  atmos- 
phere is  such  as  to  cause  even  the  planets 
to  blink  a  little,  it  has  an  effect  also  on  the 
stars.  At  such  a  time  they  will  appear  to 
be  fairly  dancing.  This  effect  is  apt  to 
occur  on  the  clear  nights  of  winter,  the 
atmosphere  being  more  unsteady  then.  Such 
nights,  because  of  the  extreme  liveliness  and 
brilliancy  that  they  lend  to  the  stars,  are 

22 


WHAT    THE    PLANETS    ARE 

attractive  times  for  amateur  observations. 
For  the  astronomer,  however,  they  are  not 
so  favorable.  For  the  seeing  of  small  de- 
tails such  as  he  seeks,  the  steadiest  atmos- 
phere is  necessary. 

Though  the  planets  are  near  enough  to 
show  a  disc,  they  are  not  sufficiently  near 
to  show  to  the  naked  eye  as  sharp  an  out- 
line as  the  moon's.  Usually  the  edge  is 
more  or  less  rayed  like  that  of  a  fixed  star, 
which  adds  somewhat  to  the  difficulty  of 
distinguishing  them  from  the  stars  until 
their  aspect  has  become  familiar  to  us.  The 
fact  that  we  are  looking  at  a  disc  is  plainly 
shown  when  an  occultation  by  the  moon 
occurs.  When  the  moon  occults  a  fixed 
star,  it  passes  between  us  and  the  star. 
At  such  times  the  star  disappears  behind 
the  edge  of  the  moon  instantly,  as  a  mere 
point  naturally  would.  When  a  planet  is 
occulted  by  the  moon,  it  disappears  gradually 
as  the  moon  covers  more  and  more  of  its 
disc,  thus  showing  unmistakably  the  nature 
of  it. 

After  steadiness  of  shining,  the  next  most 

obvious  mark  of  difference  between  a  planet 

and  a  star,  from  our  point  of  view,  is  the 

movement  of  the  planets.    A  star  remains 

23 


THE    WAYS    OF    THE    PLANETS 

always  in  one  place  with  relation  to  the  other 
xStars,  while  the  planets  move  about  from 
constellation  to  constellation,  seeming  to 
travel  sometimes  toward  the  east  and  some- 
times toward  the  west. 

This  difference  also  is  due  solely  to  a  dif- 
ference of  distance.  The  stars  as  well  as  the 
planets  are  constantly  in  motion.  Most  of 
them,  in  truth,  move  at  a  rate  which  would 
make  the  rate  of  motion  of  a  planet  a  mere 
snail's  pace  in  comparison.  Arcturus,  for 
instance,  is  supposed  to  be  moving  at  the 
rate  of  two  or  three  hundred  miles  a  second, 
and  there  are  other  fixed  stars  with  an 
equally  rapid  motion.  The  swiftest  moving 
of  the  planets  does  not  achieve  much  more 
than  twenty-nine  miles  a  second,  while  the 
slowest  swings  along  at  a  rate  of  but  little 
more  than  three  miles  in  the  same  length  of 
time. 

These  are  the  real  rates  of  speed  of  the  stars 
and  planets ;  but  they  are  not  at  all  what  they 
seem  to  us.  The  difference  in  distance  is  so 
great  that  for  centuries  and  centuries  the 
flying  stars  have  seemed  to  men  to  remain 
in  the  same  place  in  the  skies,  and  so  we  call 
them  fixed.  The  planets,  so  slow-journey- 
ing as  they  are  in  comparsion,  seem  to  us 
24 


WHAT    THE    PLANETS    ARE 

to  be  moving  among  the  constellations  at 
rates  varying  from  more  than  a  degree  a 
day  in  the  swiftest  to  between  two  and  three 
degrees  a  year  in  the  slowest. 

Hence,  if  through  lack  of  practice  in  ob-^\ 
servation  a  person  is  not  at  once  able  to  dis- 
tinguish  the    difference   between   the   stars   / 
and  the  planets  in  the  character  of  their/ 
light — that  is,  whether  they  twinkle  or  shine  >v 
steadily — he  can,  by  taking  a  little  longer    / 
time,  at  most  only  a  few  days,  determine  / 
whether  the  object  he  sees  is  a  star  or  a/ 
planet    by    noticing    whether    it    has    any 
motion  among  the  other  stars.     Venus  and 
Mars  will  show  some  movement  in  one  even- 
ing.    Jupiter  and  Saturn  may  require  a  lit- 
tle more  time  to  disclose  their  motion. 


IV 

THE    ORIGIN   OP   THE   PLANETS 

pvIFFERENT  as  the  planets  are  as  in- 
LJ  dividuals,  they  have  too  many  char- 
acteristics in  common  to  admit  any  question 
of  t?heir  common  origin.  They  are  not 
simply  stars  of  one  sort  and  another  that 
happen  to  lie  nearer  to  us  than  the  great 
body  of  stars  that  spangle  the  heavens, 
but  are,  without  doubt,  all  of  one  family  with 
us  in  their  origin,  as  well  as  in  their  situation. 
How  they  originated,  and  exactly  what  has 
been  their  course  of  evolution,  has  long  been 
an  engrossing  problem  among  philosophers; 
and  it  is  not  yet  solved. 

In  the  sense  that  the  human  race  is  all  of 
one  family,  the  planets  are  but  a  part  of  the 
great  universe  that  lies  about  us  and  is  in 
part  visible  to  us.  The  forms  in  which  we 
know  matter  as  existing  in  the  universe, 
outside  of  the  solar  system  and  of  the  minor 
forms  in  our  own  world,  are  those  of  stars 
26 


THE    ORIGIN    OF    THE    PLANETS 

and  nebulae.     It  seems  as  if  either  of  these 
could,  and  in  fact  does,  form  out  of  the  other. 
We  do  not  at  all  know  how  in  the  beginning 
matter  took  the  form  of  either,  or  which 
came  first.     But  it  is  believed  that  a  star    >" 
is  formed  by  the  condensation  of  a  nebula,  ^ 
and  that  a  nebula  is  often  formed  by  the  col- 
lision or  near  approach  of  two  stars  and  the 
consequent  disintegration  of  their  particles. 

The  sun  is  a  star  not  very  different  from 
most  of  the  other  stars,  as  we  believe  them 
to  be,  except  that  it  is  smaller  than  most  of 
them.  It  is  the  center  around  which  we 
and  all  the  planets  revolve,  and  it  is  believed 
that  we  were  all  once  a  part  of  the  very  body 
of  it.  For  astronomers  are  substantially 
agreed  that  the  whole  solar  family,  including 
the  sun  and  all  the  planets,  has  been  evolved 
from  a  great  nebula  which,  in  one  form  or 
another,  at  one  time  filled  practically  the 
whole  of  the  immense  space  from  the  sun 
to  the  outermost  planet  of  the  system. 
While  this  cannot  be  said  to  have  been  exact- 
ly proved,  yet  it  accords  with  all  the  known 
facts  of  the  solar  system.  As  to  how  this 
nebula  originated,  and  what  its  shape  was, 
and  in  just  what  way  the  planets  were  formed 
from  it,  there  is  more  diversity  of  opinion. 
27 


THE    WAYS    OF    THE    PLANETS 

Up  to  the  middle  of  the  eighteenth  cen- 
tury no  really  scientific  theory  of  the  evolution 
of  the  solar  system  was  formulated,  and  it 
was  not  until  the  very  last  years  of  that 
century  that  any  theory  of  the  origin  of  the 
planets  was  published  which  received  any- 
thing like  universal  acceptance. 

This  was  the  case,  however,  with  the  famous 
nebular  hypothesis  of  Laplace,  which  was  pub- 
lished in  1796,  and  for  a  time  seemed  so  nearly 
to  account  for  the  various  phenomena  of  the 
motions  and  relations  of  the  planets  that  it 
was  not  only  accepted  in  the  scientific  world, 
but  became  almost  as  much  a  part  of  uni- 
versal knowledge  as  that  the  earth  is  round. 
But  even  this  theory  has  not  completely 
stood  the  test  of  time,  which  inevitably 
brings  that  close  scientific  investigation  that 
any  theory  must  undergo  when  it  is  used  as 
a  working  basis  to  which  all  facts  and  sec- 
ondary theories  must  be  correlated. 

The  original  nebular  hypothesis  supposed 
this  vast  nebula  to  be  in  rotation  on  its  axis. 
As  it  condensed,  the  falling-in  of  the  particles 
caused  its  rotation  to  become  more  rapid, 
until  finally,  under  the  strain  of  this,  a  ring 
of  matter  was  ''thrown  off"  from  the  outer 
edge.  Or,  as  was  sometimes  said,  the  inner 
28 


THE    ORIGIN    OF    THE    PLANETS 

part  condensed  and  left  a  detached  ring  of 
matter.  This  ring,  continuing  to  rotate  in 
the  direction  given  it  by  the  rotation  of  the 
central  mass,  finally  condensed  into  a  planet, 
rotating  on  its  axis  and  revolving  about  the 
central  sun  in  the  same  direction  as  the  ring 
had  revolved.  The  satellites  of  the  planets 
were  thought  to  have  been  formed  by  the 
same  process  from  the  planets  while  these 
were  still  in  a  plastic  state.  Saturn,  with 
its  wonderful  system  of  rings  and  satellites, 
was  thought  to  be  a  minute  object-lesson  of 
a  planet  in  course  of  evolution,  and  this  we 
have  often  heard  said. 

I  am  sorry  it  is  not  so.  I  had  much  en- 
thusiasm in  my  youth  over  this  beautiful 
and  orderly  arrangement  of  things:  first, 
the  splendid  hypothesis,  the  achievement  of 
a  noble  mind;  then  the  little  model  showing 
the  work  in  its  progress ;  and,  finally,  the  beau- 
tifully finished  system,  the  rings  all  rolled  up 
into  planets,  traveling  unceasingly  in  paths 
which  eternally  marked  the  size  of  the  central 
body,  or  sun,  at  the  time  of  the  separation. 

But  it  is  now  pretty  certain  that  this  can- 
not be  the  way  it  all  happened.  Closer  in- 
vestigation shows  that  there  are  mechani- 
cal difficulties  which  were  not  at  first  fully 
29 


THE    WAYS    OF    THE    PLANETS 

recognized.  A  series  of  rings  could  not  have 
been  left  off  by  a  body  so  wholly  gaseous. 
The  particles  composing  them  would  not  be 
sufficiently  coherent  to  permit  of  separation 
in  any  such  compact,  uniform,  and  decisive 
manner.  Then,  even  if  such  a  ring  were 
thrown  off,  it  is  not  at  all  certain  that  it 
could  condense  into  a  planet.  Its  tendency, 
indeed,  would  be  to  disintegrate  rather  than 
to  condense.  In  a  body  so  tenuous  the  mu- 
tual gravitation  of  its  particles  would  be  too 
feeble  to  complete  the  work.  Besides,  in  con- 
flict with  the  theory  is  the  fact  that  a  few 
of  the  satellites  of  the  planets  revolve  in  a 
direction  contrary  to  that  of  the  planet.  And 
there  are  other  minor,  but  still  important, 
details  in  the  mechanism  of  the  solar  system 
which  cannot  be  accounted  for  by  the  ring 
theory. 

And  so,  while  astronomers  are  still  agreed 
at  the  whole  solar  system,  which  includes 
the  planets,  was  evolved  from  a  primeval 
nebula,  the  theory  of  leaving  off  rings  which 
condensed  into  planets  is  not  found  tenable, 
and  the  search  for  some  more  acceptable 
theory  or  some  modification  of  the  Laplace 
theory  is  now  occupying  a  number  of  emi- 
nent astronomers  and  philosophers. 
30 


THE    ORIGIN    OF    THE    PLANETS 

The  result  of  all  this  is  that  no  theory  of 
the  manner  of  the  evolution  of  the  planets 
is  definitely  accepted  by  the  body  of  astron- 
omers. Much  hard  labor  and  ingenious  rea- 
soning have  been  expended  in  endeavoring 
to  formulate  some  hypothesis  by  means  of 
which  we  may  account  for  observed  phe- 
nomena. The  astronomers  with  whom  these 
theories  have  originated  are,  naturally,  more 
or  less  ardent  in  setting  them  forth.  Thus 
one  occasionally  sees  a  decisive  and  authori- 
tative statement  of  a  theory  of  the  evolution 
of  the  planets  that  seems  at  first  view  to  ac- 
count for  everything.  But  no  one  of  these  has 
yet  been  entirely  accepted  by  astronomers, 
who  are  as  a  class  cautious  and  conservative, 
and  are  necessarily  critical  of  any  theory, 
because  the  value  of  much  of  their  future 
work  depends  upon  its  accuracy  and  suffi- 
ciency for  all  details. 

The  theory  which  at  present  seems  more 
nearly  than  any  other  to  offer  a  reasonable 
explanation  of  most  planetary  phenomena 
is  based  upon  the  supposition  that  the  nebula 
from  which  the  sun  and  planets  were  evolved 
was  in  the  shape  of  a  spiral,  and  not  the 
gaseous  mass  that  the  original  nebular  hy- 
pothesis supposed.  The  fact  that  among 


THE    WAYS    OF    THE    PLANETS 

the  many  thousands  of  nebulae  that  have 
been  discovered  and  observed  a  very  large 
proportion  of  them  are  in  this  form,  aside 
from  any  other  consideration,  suggests  a 
great  probability  that  the  one  from  which 
the  solar  system  was  evolved  was  a  spiral. 

The  spiral  nebulas  seem  to  be  of  a  some- 
what different  constitution  from  the  other 
nebulae,  and  show  on  observation  spots  of 
condensation  here  and  there,  which  at  least 
suggest  the  formation  of  systems  of  planets. 
This  indicates  that  ours  may  be  only  one  of 
many  such  systems  in  process  of  evolution; 
but  it  is  certainly  among  the  smallest  of 
them,  for  most  of  the  spiral  nebulae  are  im- 
mensely greater  in  size  than  the  one  required 
to  form  our  little  system.  Its  few  trillions 
of  miles  of  diameter,  though  it  seems  so 
vast  to  us,  is  quite  insignificant  in  com- 
parison with  a  large  proportion  of  the  spiral 
nebulae  in  the  universe. 

A  spiral  nebula  is  in  the  form  of  a  disc 
somewhat  resembling  that  familiar  form  of 
fireworks  known  as  a  pinwheel.  The  typical 
form  of  it  has  two  arms  projecting  from  op- 
posite sides  of  the  whirling  figure.  It  is 
much  denser  toward  the  center,  where  the 
spiral  would  naturally  be  more  tightly 
32 


THE    ORIGIN    OF    THE    PLANETS 

wound,  and  has  smaller  spots  of  condensa- 
tion scattered  like  knots  here  and  there 
along  the  fiery  arms.  In  the  process  of 
evolution  the  denser  center  becomes  the 
controlling  sun,  and  the  smaller  spots  of 
condensation  form  the  planets,  which  are 
eventually  detached  from  the  revolving 
mass,  but  continue  to  revolve  about  the 
center  as  they  were  doing  from  the  beginning. 
According  to  the  mass  it  has  in  the  begin- 
ning, the  planet  gathers  up  by  gravitative 
attraction  all  the  material  in  its  region,  gase- 
ous or  more  or  less  condensed,  and  grows 
by  this  accretion.  If  the  nucleus  happened 
to  be  a  large  one  before  it  separated  from 
the  parent  body,  it  will  have  sufficient  force 
of  gravitation  to  gather  in  large  quantities 
of  material  and  greatly  increase  its  size,  and 
thus  become  a  large  planet.  If  it  is  only  a 
small  nucleus,  it  has  less  power  of  attrac- 
tion, and  gathers  in  less  material. 

When  these  condensations  of  matter  which 
are  the  nuclei  of  the  planets  break  away  from 
the  parent  body,  they  sometimes  carry  with 
them  still  smaller  nuclei,  which,  if  they  are 
not  too  near  the  original  center,  or  sun,  are 
destined  to  remain  under  the  control  of  the 
planets  and  become  their  satellites.  The 
33 


THE    WAYS    OF    THE    PLANETS 

number  and  size  of  the  satellites  a  planet  has 
depends  upon  the  size,  and  hence  the  con- 
trolling force,  of  the  nucleus  which  is  its 
foundation,  and  also  upon  the  number  of 
spots  of  condensation  that  chanced  to  be 
formed  in  its  neighborhood  sufficiently  near 
to  come  under  the  gravitational  control  of 
the  planet.  If  by  any  chance  the  nucleus 
which  was  to  form  the  largest  satellite  of 
Jupiter  had  been  in  the  situation  of  Mer- 
cury, for  instance,  it  might  well  have  given 
its  allegiance  to  the  sun,  instead  of  to 
Jupiter,  and  thus  have  become  a  planet. 

Under  the  ring  theory  the  outermost 
planet,  Neptune,  would  be  the  oldest  of  the 
planet  family,  and  the  one  nearest  the  sun, 
Mercury,  would  be  the  latest  born  and  young- 
est. But  the  physical  development  of  these 
planets  seems  to  indicate,  in  truth,  exactly 
the  opposite  of  this,  as  we  shall  see  later  on. 
Under  the  spiral-nebula  theory  the  planets 
may  be  nearly  of  the  same  age,  their  differ- 
ent states  of  development  being  due  mainly 
to  difference  in  size  and  to  some  peculiarities 
of  situation.  If  the  nucleus  happened  to  be 
near  the  outer  edge  of  the  spiral,  it  would 
be  formed  from  the  lighter  matter  composing 
the  outer  part  of  the  nebula,  and  this  seems 
34 


THE    ORIGIN    OF    THE    PLANETS 

to  be  the  case  with  the  outer  planets.  If  it 
were  near  the  dense  center  of  the  nebula,  it 
would  be  composed  of  denser  material,  and 
this  seems  to  be  so  in  the  case  of  the  inner 
planets. 

A  nebula,  it  is  thought,  is  formed  by  the 
collision  or  the  near  approach  of  two  of  the 
many  stars,  or  suns,  that  we  know  are 
traveling  about  at  high  velocities  as  va- 
grants here  and  there  through  space.  If 
the  two  bodies  come  together  centrally,  the 
force  of  the  impact  will  generate  heat  suffi- 
cient to  convert  them  into  a  nebula;  but 
this  will  not  necessarily  be  spiral  in  form. 
If  they  come  together  obliquely,  the  chances 
are  that  they  will  form  into  a  rapidly  rotat- 
ing spiral  disc. 

But  in  order  to  form  a  spiral,  it  is  not 
necessary  that  there  should  be  an  actual 
collision.  Because  of  the  force  of  gravita- 
tion the  near  approach  of  two  stars  would 
subject  them  to  an  enormous  strain  from 
their  pull  upon  each  other,  and  there  is  a 
limit  within  which  they  cannot  approach 
without  being  literally  torn  to  pieces  from 
the  effect  of  this  tidal  force.  Even  if  they 
do  not  approach  within  this  fatal  limit, 
4  35 


THE    WAYS    OF    THE    PLANETS 

which  is  a  little  less  than  two  and  one-half 
times  the  radius  of  the  body,  they  may  come 
so  near  as  to  change  their  character  entirely, 
and,  through  their  tidal  influence  on  each 
other,  form  into  a  rotating  spiral  nebula 
with  two  arms  projecting  from  opposite 
sides  of  the  spiral. 

It  now  seems  probable  that  it  was  after 
this  manner  that  the  sun  and  its  family  of 
planets  were  formed.  The  matter  which  is 
contained  in  them  may  have  been  in  the 
form  of  a  dark,  solid  body  pursuing  some  sort 
of  course  in  space.  In  its  journeying  it  came 
near  another  body  and  was  awakened  into 
a  life  of  activity  in  the  form  of  a  flat,  spiral 
nebula  which  was  left  spinning  around  in  a 
pyrotechnic  manner,  the  matter  composing 
it  much  diffused  at  the  outer  edges  and  dens- 
est in  the  center.  Scattered  through  it  were 
the  more  or  less  condensed  spots  which  were 
the  embryonic  forms  destined  to  come  forth 
from  the  parent  body  as  the  individual 
planets. 

When  the  separation  was  completed,  each 
planet  fed  and  grew  upon  all  the  matter  that 
it  had  the  force  to  draw  to  it,  and  it  swept 
clean  the  space  that  lay  within  the  limits 
of  its  power.  If  the  particles  thus  gathered 
36 


THE    ORIGIN    OF    THE    PLANETS 

in  were  small  and  slow  of  motion,  they  be- 
came a  part  of  the  body  of  the  planet.  If 
they  were  large  and  swift,  they  became 
members  of  the  planet's  family  as  satellites. 
In  whatever  area  of  the  nebula  each  planet 
came  into  a  separate  existence,  it  fed  upon 
the  matter  which  that  area  afforded.  In 
the  case  of  Neptune,  at  the  outer  edge  of 
the  system,  it  was  very  diffuse  matter;  in 
Mercury's  region,  nearer  the  center,  it  was 
more  dense. 

Thus  in  our  family  of  planets,  though  its 
members  were  born  of  the  same  parent  and 
developed  under  the  same  guiding  laws, 
each  has  a  distinct  individuality  arising 
from  its  inherent  qualities  and  its  environ- 
ment during  the  early  stages  of  its  existence. 
The  spiral-nebula  theory  seems  to  offer  a 
better  explanation  of  these  individual  quali- 
ties than  any  other  that  has  been  advanced 
thus  far,  and  in  its  main  features  it  is  pretty 
generally  accepted.  But  one  must  keep  in 
mind  that  the  details  of  any  theory  of  the 
beginning  and  growth  of  the  planets  are 
more  or  less  speculative,  or,  at  least,  have  not 
yet  been  proved  with  finality. 


THE  SEVEN  GREAT  PLANETS 

SO  far  as  we  know,  five  of  the  planets — 
Mercury,  Venus,  Mars,  Jupiter,  and 
Saturn — have  been  known  from  time  im- 
memorial. There  are  existing  records  of 
them  made  thousands  of  years  ago.  There 
is  no  reason  why  they  should  not  have  been 
thus  known,  since  they  have  always  been 
as  they  are  now,  visible  to  the  naked  eye, 
and  all  of  them  save  Mercury  are  as  easily 
seen  as  the  sun  or  the  moon.  They  do  not, 
of  course,  exact  the  instant  attention  that 
those  great  luminaries  do,  because,  being 
smaller,  they  are  less  isolated  from  the  great 
body  of  the  stars;  but  they  are  in  their 
seasons  plainly  visible,  and  can  then  always 
be  seen  if  one  looks  at  them. 

In  ancient  times,  when  people  lived  more 
out-of-doors  than  is  the  habit  now,  they  did 
look  at   them.     The   same  primitive  shep- 
herds  that,    while   tending   their   flocks   at 
38 


THE  SEVEN  GREAT  PLANETS 

night  on  the  hills,  named  the  constellations 
according  to  the  fanciful  shapes  that  the 
unchanging  stars  seemed  to  outline,  watched 
also  the  five  wandering  stars,  more  wonder- 
ful to  them  than  any  of  the  others.  They 
observed  how  mysteriously  these  stars  came 
at  certain  seasons  and  silently  threaded  their 
way  across  the  shining  heavens,  and  then  as 
mysteriously  disappeared.  They  saw  them 
not  only  differing  from  the  other  stars  in 
glory,  but  changing  in  their  own  brilliancy 
from  one  time  to  another,  until,  in  some  cases, 
they  failed  to  recognize  them  as  the  same 
stars  under  varying  aspects.  Venus,  for 
instance,  they  called  Phosphorus,  or  Lucifer, 
when  they  saw  her  as  a  morning  star,  and 
Hesperus,  or  Vesper,  when  she  shone  in  the 
evening. 

The  sun  and  the  moon,  they  noted,  also 
moved  from  place  to  place  among  the  fixed 
stars,  and  they  called  all  these  errant  bodies 
planets,  which  means  "wanderers."  These 
are  the  "seven  planets"  referred  to  in  the 
earlier  literatures  and  in  all  early  books 
on  astronomy  or  astrology.  This  is  some- 
times a  little  confusing,  because,  though  the 
sun  and  the  moon  are  no  longer  called 
planets,  we  still  (omitting  the  earth)  have 
39 


THE    WAYS    OF    THE    PLANETS 

seven.  But  Neptune  and  Uranus,  not  being 
visible  to  the  naked  eye,  were  not  known 
to  the  ancients.  They  were  discovered  by 
means  of  the  telescope,  and  that  only  within 
the  last  century  and  a  half.  So,  owing  to 
these  comparatively  new-found  members  of 
the  solar  family,  we  have  yet  the  magic 
number  of  planets,  seven. 

These  seven  are  the  major  planets  and  the 
ones  with  which  mainly  it  will  be  our  en- 
deavor here  to  promote  and  strengthen  an 
acquaintance.  With  Uranus  and  Neptune 
the  acquaintance  will  necessarily  be  less  in- 
timate than  with  the  others,  because  we  can- 
not see  them  in  the  same  free  way;  but 
they  are  not  on  this  account  much  less  in- 
teresting than  the  others,  and  a  little  knowl- 
edge of  them  is  pleasant  family  history. 
They  simply  do  not  live  within  sight. 

The  planets  that  are  nearer  to  the  sun 
than  we  are,  and  hence  lie  between  us  and 
the  sun,  are  called  the  inferior,  or  sometimes 
interior,  planets.  Those  that  lie  outside 
the  orbit  of  the  earth  are  called  the  superior, 
or  the  exterior,  planets.  In  so  grouping 
them  the  earth  is  the  dividing-point,  and  is 
not  itself  in  either  class.  Mercury  and 
Venus  are  the  inferior  planets.  The  superior 
40 


THE  SEVEN  GREAT  PLANETS 

planets  are  Mars,  Jupiter,  Saturn,  Uranus, 
and  Neptune.     The  distinction  has  impor- 
tance, especially  when  we  are  discussing  the 
planets  with  relation  to  their  movements, 
as  seen  from  the  earth,  because  the  planets        .X 
with  orbits  between  us  and  the  sun  (the  in-   ^ 
ferior  planets)   have  very   different  phases 
and    apparent    motions    from    those    whose 
orbits  are  beyond  us  from  the  sun  (the  su- 
perior planets). 

When  considered  in  regard  to  size,  con- 
stitution, development,  and  their  likeness  to 
each  other,  the  planets  are  sometimes  dis- 
tinguished as  the  terrestrial  planets  and  the 
major  planets.  This  need  occasion  no  con- 
fusion with  the  general  division  of  them  into 
major  and  minor  planets,  because,  as  has 
been  said,  when  simply  "the  planets"  are 
mentioned,  these  seven  large  planets  are 
always  the  ones  that  are  meant,  the  others 
being  usually  called  asteroids,  or  planetoids. 
The  terrestrial  planets  are  Mercury,  Venus, 
Earth,  and  Mars.  As  the  name  implies, 
they  are  so  called  because  they  are  in  somei 
respects  similar  to  the  earth.  The  major 
planets  are  Jupiter,  Saturn,  Uranus,  and 
Neptune.  They  are  all  larger  than  the  ter- 
restrial planets,  and,  in  addition,  have  some 
41 


THE    WAYS    OF    THE    PLANETS 

other  characteristics  in  common  which  the 
planets  of  the  other  group  do  not  have.  The 
two  classes  represent  different  stages  of  evo- 
lution. 

The  four  planets  forming  the  terrestrial 
group  are  sometimes  called  the  inner  planets, 
and  the  four  major  planets  are  then  known 
as  the  outer  planets.  The  point  of  division 
in  mind  then  is  the  space  between  Mars  and 
Jupiter.  This  is  so  vast  in  comparison  with 
the  spaces  between  the  other  planets  from 
the  sun  out  to  Mars  that  it  becomes  a 
convenient  dividing-line,  particularly  as  the 
groups  divided  by  it  are  in  some  respects 
essentially  different  from  each  other. 

Of  the  four  planets  which  have  an  especial 
interest  to  us  because  of  their  being  the  ones 
most  easily  seen,  two  are  terrestrial,  or  inner, 
planets,  Mars  and  Venus,  and  two  are  major, 
or  outer,  planets,  Jupiter  and  Saturn.  The 
differences  between  the  two  classes  are  sole- 
ly matters  of  constitution  and  situation,  and 
have  nothing  to  do  with  their  appearance 
to  us.  Venus,  the  brightest  of  them  all,  be- 
longs to  one  group;  Jupiter,  the  second  in 
brilliancy,  belongs  to  the  other. 

That  there  is  at  least  one  other  planet 
beyond  the  present  boundary  of  our  system 
42 


THE  SEVEN  GREAT  PLANETS 

(which  is  the  orbit  of  Neptune)  seems  to  be 
quite  probable.  Some  astronomers  think 
there  may  be  several  others.  There  are  cer- 1^ 
tain  perturbations,  or  irregularities,  in  the 
movements  of  Neptune  which  the  influence 
of  Uranus  does  not  account  for,  and  they 
seem  to  indicate  that  there  is  some  disturb- 
ing body  even  beyond  the  orbit  of  that 
farthest  known  planet. 

Several  astronomers  are  working  on  the 
problem  of  locating  this  undiscovered  body. 
At  various  times  it  has  been  announced  that 
such  a  planet  would  probably  be  found  in  a 
certain  position  in  the  skies  at  a  specified 
date;  but  as  yet  no  one  has  been  able  to 
get  a  view  of  it.  Recently  the  orbit  of  a  far- 
off  hypothetical  planet  has  been  calculated, 
and  its  place  predicted  for  1914.  Perhaps 
it  may  be  found  then.  Of  course  it  could 
never  be  seen  through  any  but  the  most 
powerful  telescopes.  Its  calculated  distance 
from  the  sun  is  one  hundred  and  five  times 
that  of  the  earth.  This  would  be  more  than 
nine  billions  of  miles,  or  more  than  three 
times  farther  than  Neptune  is  from  the  sun. 
It  would  require  fourteen  hours  for  light 
to  pass  from  the  sun  to  a  planet  at  that 
distance,  and  the  sun  would  appear  to  it 
43 


THE    WAYS    OF    THE    PLANETS 

smaller  than  Saturn  or  an  ordinary  first- 
magnitude  star  does  to  us. 

A  further  reason  for  suspecting  the  exist- 
ence of  such  a  planet  is  suggested  by  the 
orbits  of  certain  comets.  These  erratic 
bodies,  when  they  chance  to  come  within 
the  bounds  of  the  solar  system,  are  some- 
times forced  to  remain  because  of  the  power- 
ful influence  of  one  of  the  planets  near  which 
their  path  has  taken  them.  Jupiter  holds 
as  many  as  thirty  of  them  in  this  way, 
Saturn  and  Uranus  have  two  or  three,  and 
Neptune  has  captured  as  many  as  six.  But 
there  are  still  others  that  return  to  us  in 
regular  periods,  but  which  go  sufficiently  far 
beyond  Neptune  to  escape  entirely  if  there 
were  not  some  still  more  distant  watch-dog 
to  turn  them  back.  So  there  seems  good 
reason  to  believe  that  Neptune  is  not  really 
the  outermost  of  the  planets. 

There  has  also  been  much  said  about  the 
possibility  of  a  planet  nearer  to  the  sun  than 
Mercury.  When  Mercury  is  at  perihelion, 
or  nearest  to  the  sun,  there  are  certain  ir- 
regularities in  his  movements  which  might 
be  explained  by  the  presence  of  another 
planet  between  Mercury  and  the  sun.  In 
1859  it  was  thought  that  such  a  planet  had 
44 


THE  SEVEN  GREAT  PLANETS 

been  observed.  Its  time  of  revolution  and  its 
distance  from  the  sun  were  estimated,  and  it 
was  named  Vulcan.  In  some  of  the  books  of 
astronomy  published  about  that  time,  and 
even  in  some  published  as  many  as  fifteen 
years  later,  Vulcan  is  mentioned  as  a  reality. 
But  now  it  is  believed  that  the  observation 
was  a  mistake,  and  no  such  body  is  known 
to  exist. 

In  1 878  it  was  again  thought  that  two  bodies 
nearer  to  the  sun  than  Mercury  had  been  dis- 
covered during  an  eclipse.  These  observa- 
tions have  never  been  explained  or  confirmed; 
but  it  is  thought  that  the  objects  seen  were 
probably  stars  which  were  mistaken  for 
planets  by  the  observers.  If  a  body  so  sit- 
uated does  exist,  it  is  so  near  the  sun  that 
it  probably  can  never  be  seen  except  during 
an  eclipse,  and  the  time  of  observation  is 
then  so  short  and  mistakes  are  so  easily 
made  that  it  is  difficult  to  verify  the  obser- 
vation. The  continued  search  for  the  cause 
of  the  perturbations  of  Mercury  may  finally 
lead  to  the  discovery  of  something  between 
it  and  the  sun.  But  if  it  is  a  single  body, 
this  seems  a  much  less  promising  task  than 
the  search  for  a  planet,  or  planets,  on  the 
outer  edge  of  the  solar  system. 


VI 

THE   MOVEMENTS    OF  THE   PLANETS 

IN  considering  the  movements  of  the  plan- 
ets, we  have  to  regard  their  actual  mo- 
tion in  space  and  that  motion  as  it  ap- 
pears to  us.  They  all  have  two  principal 
motions  in  space.  They  revolve  about  the 
.xSun  in  their  orbits,  and  they  rotate  on  their 
axes.  The  manner  in  which  they  accom- 
plish the  rotation  on  their  axes  determines 
the  length  of  their  days  and  nights,  or 
whether,  indeed,  they  shall  have  any  such 
grateful  alternations  of  light  and  darkness. 
Those  planets  which,  like  the  earth,  turn  on 
their  axes  in  less  time  than  they  make  their 
journey  around  the  sun  have  one  day  and 
one  night  every  time  they  make  a  complete 
rotation.  Those  that  turn  on  their  axes  in 
the  same  time  that  they  revolve  around  the 
sun,  of  which  sort  there  seems  to  be  at  least 
one,  face  always  toward  the  sun,  and  have 
no  alternations  of  day  and  night.  On  one 
46 


MOVEMENTS    OF   THE    PLANETS 

side  it  is  always  day;  on  the  other  it  is 
always  night.  The  number  of  days  a  planet 
has  during  each  revolution  around  the  sun 
depends  upon  how  much  time  it  requires  to 
make  a  revolution,  and  how  fast  it  spins  on  its 
axis.  In  one  year  here  on  the  earth  we  have 
three  hundred  and  sixty-five  days  and  nights. 
Saturn,  in  its  year,  has  more  than  twenty- 
three  thousand  days  and  nights. 

The  manner  in  which  the  revolution  of 
the  planets  in  their  orbits  takes  place  deter- 
mines the  length  and  character  of  their  year; 
the  nearer  a  planet  is  to  the  sun,  the  shorter , 
its  orbit  is,  and  the  faster  the  rate  of  speed 
at  which  the  sun  compels  it  to  move,  and 
hence  the  shorter  its  year.  The  nearest  of 
the  planets,  Mercury,  makes  more  than  five 
hundred  revolutions  around  the  sun,  while  *^* 
the  farthest,  Neptune,  makes  one.  Three 
times  in  a  year — that  is,  a  terrestrial  year — 
the  nearest  planet  speeds  around  its  orbit 
and  back  to  the  starting-place  with  seventeen 
days  to  spare.  One  hundred  and  sixty-five 
terrestrial  years  are  necessary  for  the  farthest 
planet  to  make  one  circuit  of  its  orbit.  The 
first  goes  at  the  average  rate  of  nearly  thirty 
miles  a  second  over  a  path  more  than  two 
hundred  million  miles  long.  The  second 
47 


THE    WAYS    OF    THE    PLANETS 

travels  a  path  more  than  seventeen  billion 
miles  in  length,  at  the  average  rate  of  three 
and  four- tenths  miles  a  second.  Between 
these  two  extremes  the  other  planets  have 
orbits  and  rates  of  speed  varying  with  their 
s  distances  from  the  sun.  Toe  farther  they  are 
from  the  sun,  the  larger  the  orbit  and  the 
slower  the  speed. 

To  get  something  like  a  picture  of  the  sun 
and  the  planets  as  they  actually  lie  and  as 
they  move  in  space,  one  should  have  in  mind 
an  immense  flat,  circular  disc  five  and  a  half 
billions  of  miles  in  diameter  passing  through 
the  sun,  which  is  in  the  center  of  it.  Around 
the  edge  of  the  disc  is  the  orbit  through 
which  Neptune  moves.  At  varying  dis- 
tances inside  of  it  are  the  orbits  of  the  other 
planets,  eaeli  ^rowiii^  smaller  and  smaller 

as  one  comes  nearer  and  nearer  to  the  sun, 
until  the  orbit  of  Mercury,  the  planet  nearest 
to  the  sun,  is  reached. 

Since  it  is  not  a  hard  metal  disc  that  we 
are  considering,  but  only  an  imaginary  one 
in  space,  there  may  be  a  little  latitude  al- 
lowed for  the  orbits  to  tip  somewhat  out  of 
the  exact  plane  of  the  disc  without  materially 
altering  the  figure  in  mind.  And  this  they 
do,  very  slightly — most  of  them  to  the  ex- 
48 


MOVEMENTS    OF    THE    PLANETS 

lent,  only  of  from  one  to  1  wo  drives,  thorn-;!! 
one  of  them  falls  outside  of  the  common 
plane  about  seven  degrees.  In  these  orbits 
all  the  planets,  as  seen  from  the  sun,  are 
i'.oinjir  ;in>tiM(1  from  west,  to  r;isl.  Af.  tlir 
same  time  they  are  turning  on  their  axes  in 
the  same  direction,  some  standing  almost 
erect,  as  it  were,  in  their  orbits  and  whirling 
like  a  dancing  dervish  as  they  skim  along, 
and  others  more  or  less  inclined  like  a 
traveling  top. 

The  time  a  planet  requires  to  make  one 
circuit  of  its  orbit  constitutes,  as  with  the 
earth,  its  year.  But  we  who  are  on  the  earth 
have,  in  our  study  of  another,  planet,  to  re- 
gard it  as  having  in  a  sense  two  years.  First, 
there  Is  the  time  it  takes,  starting  from  a 
given  point  in  its  orbit,  to  circle  around  the 
sun  and  return  to  that  point.  This  is  known 
as  its  sidereal  period,  or  year,  and  is  so  called 
from  si'dws,  meaning  a  star,  because  the  only 
way  to  mark  any  point  in  space  is  by  a  fixed 
star,  and,  as  viewed  from  the  sun,  one  revo- 
lution of  a  planet  would  be  from  a  given 
star  back  again  to  that  star. 

Then  there  is  the  time  a  planet  takes, 
starting  when  it  is  in  a  straight  line  with  the 
earth  and  the  sun  in  space,  to  return  to  the 
49 


THE    WAYS    OF    THE    PLANETS 

place  where  the  three  bodies  will  be  again 
in  the  same  relative  position.  This  is  known 
as  its  synodic  period,  or  year.  Synodic  is 
from  our  word  synod,  meaning  a  meeting 
JOT  assembly,  and  the  synodic  year  is  the  time 
^/between  two  successive  and  similar  meetings 
of  these  three  bodies.  The  sidereal  year  con- 
cerns the  planet  in  its  relation  to  the  sun; 
the  synodic  year,  in  its  relation  to  the  earth. 
The  synodic  year  is  the  only  one  that  much 
concerns  us  while  regarding  the  planets  as 
a  part  of  the  spectacle  of  the  sky.  It  is  the 
one  that  we  know  from  observation,  while 
the  sidereal  year  is  mathematically  com- 
puted. 

The  two  periods,  or  years,  are  not  of  the 
same  length,  because  the  sun  with  reference 
to  the  planet  is  always  stationary,  and  the 
motion  resulting  in  the  sidereal  year  is  that 
of  the  planet  only,  while  the  synodic  year 
is  the  result  of  the  movements  of  both  the 
earth  and  the  planet,  each,  in  its  own  orbit, 
being  always  in  motion. 

An  inferior  planet,  situated  as  it  is  nearer 
to  the  sun  than  the  earth  is,  and  so  having  a 
shorter  orbit  than  the  earth's,  will,  when  it 
finishes  its  sidereal  year  and  comes  around 
to  the  point  from  which  it  started,  find  the 
50 


MOVEMENTS    OF    THE    PLANETS 

earth  advanced  from  that  position  and  will, 
therefore,  have  to  travel  farther  on  in  order 
to  overtake  it  and  come  into  the  same  rela- 
tive position  from  which  they  started,  which 
makes  the  time  of  its  circuit  with  reference 
to  the  earth  obviously  longer  than  with 
reference  to  the  sun. 

With  the  superior  planets  the  case  is  just 
reversed.  The  earth  is  the  inside  planet, 
or  the  one  nearest  the  sun,  and  it  must  over- 
take them.  With  one  exception,  they  are  all 
so  far  away  from  the  sun  and  move  so  slowly 
that  it  takes  us  but  little  more  than  one  of 
our  years  to  overtake  them  and  bring  them 
into  the  same  relative  position  with  us  that 
they  had  when  we  started,  while  it  requires 
many  of  our  years  for  any  one  of  them  to 
make  a  single  circuit  of  the  sun.  Hence 
their  circuit  with  reference  to  the  earth  is 
shorter  than  with  reference  to  the  sun. 

With  Mars,  the  exception  referred  to,  we 
have  a  more  hardly  fought  race.  That 
planet  is  not  so  far  from  us  as  are  the  other 
superior  planets.  It  makes  its  revolution 
around  the  sun  in  a  little  less  than  two  of 
our  years.  We  travel  eighteen  miles  a  sec- 
ond, and  it  travels  fifteen  miles  in  the  same 
length  of  time.  If  we  are  in  line  with  it  at 

5  51 


ear 

\^T7Pa 


THE    WAYS    OF    THE    PLANETS 

the  beginning  of  our  journey,  we  glide  off 
swiftly,  and  easily  leave  it  far  behind.  When, 
however,  we  come  back  to  the  starting- 
point,  it  has  not  loitered,  and  is  many  millions 
of  miles  ahead  of  us,  and  it  remains  ahead 
until  more  than  seven  weeks  after  we  have 
returned  to  the  starting-point  a  second  time. 
Fifty  days  after  we  have  begun  to  make  our 
third  round  we  overtake  it,  and  are  again 
in  a  direct  line  with  the  planet  and  the  sun. 
This  makes  its  period  with  reference  to  the 
th  ninety-three  days  longer  than  its  own 
year,  and  fifty  days  longer  than  two  of  ours. 
This  is  the  longest  synodic  period  among 
the  planets. 

The  orbits  in  which  the  planets  move  all 
have  the  form  of  an  ellipse — that  is,  of  a 
circle  more  or  less  flattened.  This  flattening, 
or  the  extent  to  which  an  orbit  departs  from 
the  form  of  a  true  circle,  is  called  its  eccen- 
tricity. The  sun  is  never  at  the  exact  center 
of  an  orbit,  but  is  always  situated  a  little  to 
one  side  of  the  center — that  is,  it  is  at  one 
of  the  foci  of  the  ellipse.  Consequently,  the 
planet,  as  it  travels  in  its  orbit,  is  not  always 
at  the  same  distance  from  the  sun,  the  amount 
of  the  variation  in  distance  depending  upon 
the  eccentricity  of  the  orbit.  The  point  in 
52 


MOVEMENTS    OF    THE    PLANETS 

the  orbit  where  the  planet  is  nearest  to  the 
sun  is  its  perihelion,  and  the  point  at  which 
it  is  farthest  is  its  aphelion.  It  is  necessary 
to  keep  these  elementary  facts  in  mind  in 
order  fully  to  understand  the  changes  in  the 
motions  and  brightness  of  the  planets. 

The  influence  of  one  body  over  another 
that  is  circling  around  it  is  to  make  it  move 
faster  or  more  slowly  according  to  its  dis- 
tance from  the  central  body.  Since  a  planet 
varies  in  its  distance  from  the  sun  in  the 
different  parts  of  its  orbit,  it  is  forced  to 
move  fastest  when  it  is  in  that  part  of  the 
orbit  which  is  nearest  to  the  sun,  and  slow- 
est when  it  is  in  the  part  farthest  away.  In 
other  words,  the  motion  of  a  planet  is  more 
rapid  at  perihelion  than  at  aphelion.  The 
earth  is  in  perihelion,  or  nearest  to  the  sun, 
in  winter  —  that  is,  winter  in  the  northern 
latitudes — and  in  consequence  it  moves 
faster  in  winter  than  in  summer,  and  the 
northern  winters  are,  for  this  reason,  a  little 
shorter  than  the  summers. 

These  two  simple  movements  of  the 
planets — that  around  the  sun  and  that  on 
their  axes — are  their  principal  real  move- 
ments, and  are  such  as  they  would  show  to 
be  if  seen  from  the  sun,  which  is  the  center 
53 


THE    WAYS    OF    THE    PLANETS 

of  them.  There  are  also  certain  minor  real 
movements  arising  from  various  causes,  one 
being  the  influence  that  the  planets  exercise 
on  one  another;  but  for  the  ordinary  observer 
these  have  no  particular  significance.  Then, 
the  planets  all  share  the  one  grand  move- 
ment which  the  sun  itself  is  known  to  be 
making  through  limitless  space  to  a  destina- 
tion of  which  we  are  in  utter  ignorance,  over 
even  a  path  which  we  know  nothing  of  save 
that  it  leads  toward  the  bright  star  Vega, 
in  the  constellation  of  the  Lyre.  As  the  sun 
moves  on  in  that  direction  at  the  rate  of 
eleven  miles  a  second  he  takes  with  him  all 
his  family  of  planets  and  planetoids,  with 
their  satellites,  and  whatever  other  bodies 
have  their  abode  in  his  domain.  Thus  they 
travel  as  a  body,  each  individual  spinning 
on  its  axis,  from  the  sun  itself  down  to  the 
smallest  planetoid,  the  satellites  circling 
\  around  the  planets,  and  the  planets  in  their 
turn  around  the  sun.  And  in  all  these 
movements  the  earth  takes  part  as  one  of 
the  planets.  The  sun  itself  is  following  a 
comparatively  straight  line  in  space,  and,  so 
far  as  we  know,  in  allegiance  to  no  other 
body.  It  is,  though,  just  possible  that  this 
comparatively  straight  line  may  be  the  arc 
54 


MOVEMENTS    OF    THE    PLANETS 

of  a  circle  so  vast  that  we  have  not  yet 
had    time    to    discover   its    curvature,   and        .X 
that   the    sun    itself    may  be    pursuing   its   ^ 
own  circuit  around  some  still  more  powerful 
body. 


VII 

HOW  THE    INFERIOR  PLANETS   SEEM  TO   MOVE 

OF  the  real  movements  of  the  planets, 
as  described  in  the  last  chapter,  we 
get  here  on  the  earth  only  a  very  fragmen- 
tary view.  Without  the  aid  of  the  telescope 
none  of  them  is  visible  to  us  except  the 
movements  in  their  orbits,  and  these,  to  our 
view,  are  somewhat  different  from  the  sim- 
ple, circling  course  apparent  to  an  observer 
on  the  sun.  The  difference  is  due  to  the 
fact  that  the  earth  itself  is  always  in  move- 
ment in  just  the  same  way  that  the  other 
planets  are,  and  we,  being  never  at  any  time 
at  the  center  of  the  orbits,  do  not  see  the 
movements  of  the  planets  as  they  truly 
take  place,  but  only  as  they  are  outlined 
against  the  sky.  So  the  appearances  and 
disappearances  and  visible  travels  among 
the  stars  by  which  we  know  the  planets  are 
only  as  we  see  them.  Some  knowledge  of 
the  real  movements  is  necessary  to  a  proper 
56 


INFERIOR  PLANETS:  SEEMING  MOTION 

understanding  of  the  apparent  movements; 
but  it  is  only  with  the  latter  that,  for  ordi- 
nary observation,  we  need  to  be  particularly 
acquainted. 

The  rotation  of  the  earth  on  its  axis,  as 
we  know,  causes  the  familiar  daily  apparent 
rising,  passing,  and  setting  of  all  the  heav- 
enly bodies.  In  this  apparent  motion  the 
planets  share  as  well  as  the  sun,  moon,  and 
stars.  But  it  is  their  movement  among  the 
fixed  stars,  and  not  with  them,  that  distin- 
guishes them  as  planets,  and  this  it  is  neces- 
sary to  know  in  order  to  keep  track  of  them 
and  be  able  to  recognize  them  in  their  vary- 
ing places  and  guises.  For  they  sometimes 
shine  in  their  greatest  glory  in  one  season, 
and  sometimes  in  another,  and  at  the  re- 
currence of  the  same  season  they  are  some- 
times in  one  part  of  the  sky  and  sometimes 
in  another,  so  that  their  ways  of  coming  and 
going  border  almost  on  the  mysterious,  until 
one  learns  the  manner  of  this  apparent 
vagrancy.  Happily,  this  knowledge  is  easily 
attained,  and  then  the  matter  is  simple 
enough. 

The  apparent  motions  of  the  inferior 
planets,  Mercury  and  Venus,  always  take 
place  near  the  sun.  Venus  never  wanders 
57 


THE    WAYS    OF    THE    PLANETS 

more  than  forty-eight  degrees  from  it,  and 
^Mercury  never  more  than  twenty-eight. 
Most  of  the  time  they  are  much  nearer  than 
this.  Since  we  cannot  see  either  of  them 
except  when  the  sun  is  below  the  horizon, 
the  consequence  of  their  being  always  thus 
near  to  him  is  that  they  are  in  view  for  only 
a  short  time  after  the  sun  has  set  or  before 
he  has  risen.  If  they  are  in  the  evening 
sky,  and  hence  east  of  the  sun,  they  soon 
follow  him  when  he  sinks  below  the  western 
horizon.  If  they  are  west  of  the  sun,  and, 
consequently,  are  the  first  to  rise  in  the 
morning,  it  is  not  long  before  his  brilliant 
rays  flood  with  light  the  eastern  sky  and  blot 
the  planets  from  our  view.  Venus  can  be 
seen  sometimes  for  three  hours  at  a  time, 
Mercury  for  never  more  than  one.  Within 
this  limited  region  of  the  sky  they  appear 
to  journey  evening  by  evening  away  from 
the  sun,  somewhat  obliquely,  but  toward 
the  zenith,  until  they  have  reached  the  end 
of  their  tether.  Then  they  journey  back  and 
pass  to  the  other  side  of  the  sun.  There 
they  climb  their  path  toward  the  zenith, 
moving  westward  and,  as  we  see  them,  ob- 
liquely upward.  Morning  by  morning  they 
get  farther  from  the  sun  until  their  west- 
58 


INFERIOR  PLANETS:  SEEMING  MOTION 

ward  limit  of  freedom  is  reached,  when  they 
again  draw  in  toward  the  sun,  pass  it,  ap- 
pear in  the  evening  sky,  and  pull  off  up  the 
sky  toward  the  east  again.  Thus  they  swing 
from  east  to  west  of  the  sun,  and  back  again, 
in  unceasing  repetition. 

As  they  pass  the  sun  going  from  east  to 
west — that  is,  from  the  evening  to  the  morn- 
ing sky — the  inferior  planets  go  between  us 
and  the  sun;  and  when  they  swing  back 
from  west  to  east,  or  from  the  morning  to 
the  evening  sky,  they  pass  on  the  side  of  the 
sun  farthest  away  from  us.  When  they  are 
in  a  direct  line  with  the  earth  and  the  sun 
they  are  said  to  be  in  conjunction.  If  at 
this  point  they  are  between  us  and  the 
sun,  it  is  inferior  conjunction.  If  they  are 
on  the  other  side  of  the  sun,  they  are  said 
to  be  in  superior  conjunction.  When  the 
planet,  as  seen  in  the  evening,  has  traveled 
toward  the  east  as  far  from  the  sun  as  it 
will  go  during  that  particular  revolution,  it 
is  said  to  be  at  its  greatest  eastern  elonga- 
tion. Elongation  means  simply  apparent 
distance  from  the  sun;  hence,  greatest  east- 
ern elongation  is  the  greatest  distance  pos-  v  / 
sible  east  of  the  sun  from  our  point  of  view.  ^ 
Greatest  western  elongation,  which  we  see 
59 


THE    WAYS    OF    THE    PLANETS 

in  the  morning  before  dawn,  occurs  when 
the  planet  is  at  its  greatest  apparent  dis- 
tance west  of  the  sun. 

While  apparently  drawing  near  and  then 
away  from  the  sun,  traveling  obliquely  up 
and  down  the  evening  and  the  morning  sky, 
the  planet  has  all  the  time  been  moving  in 
one  direction  around  the  sun;  but  we  could 
see  the  motion  only  as  it  appeared  on  the 
background  of  the  sky.  The  planet  is  in 
reality  just  as  far  from  the  sun  when  it  is 
in  conjunction  as  at  elongation.  The  dif- 
ference is  that  we  see  it  at  a  different  angle, 
or  from  a  different  point  of  view.  But  it  has 
not  been  at  all  times  equally  near  to  the 
earth. 

When  an  inferior  planet  is  at  greatest 
eastern  elongation,  it  is,  of  course,  east  of 
the  sun,  and  can  be  seen  above  the  sun  in 
the  evening  after  sunset,  and  is  an  evening 
star.  As  it  moves  westward  nearer  and 
nearer  to  the  sun,  it  is  above  the  horizon  a 
proportionately  shorter  time  each  evening, 
and  is  more  and  more  obscured  by  the  sun's 
rays  until  it  reaches  inferior  conjunction, 
when  it  is  exactly  between  us  and  the  sun, 
and  hence  at  the  point  nearest  to  us.  Here 
it  becomes  invisible,  largely  because  it  has 
60 


INFERIOR  PLANETS:  SEEMING  MOTION 

its  dark  side  toward  us,  but  partly  because 
the  dazzling  light  of  the  sun  entirely  obscures 
it.  Once  in  a  while  our  relative  positions  are 
such  that  we  see  it  pass  like  a  black  dot 
directly  over  the  bright  face  of  the  sun. 
This  is  called  a  transit.  But  a  transit  does 
not  occur  at  every  inferior  conjunction.  It 
would  so  occur  if  the  planet's  orbit  and 
the  earth's  were  in  exactly  the  same  plane. 
But  the  small  tilt  that  they  have  is  sufficient 
to  throw  the  planet,  when  it  is  passing  the 
sun,  into  such  an  angle  that  it  does  not  pass 
directly  between  the  d^sc  of  the  sun  and  us, 
but  a  little  above  or  below.  Thus  transits 
are  rather  rare,  though  they  occur  periodi- 
cally in  the  case  of  both  Venus  and  Mercury, 
and  will  be  spoken  of  elsewhere. 

When  the  planet  has  passed  inferior  con- 
junction, it  is  then  west  of  the  sun,  and  rises 
in  the  morning  before  the  sun  is  up,  and  is 
a  morning  star.  For  a  few  days  it  can  be  s 
seen  either  not  at  all  or  with  difficulty. 
Then,  as  it  works  its  way  out  of  the  rays  of 
the  sun  and  on  toward  the  west,  it  rises 
earlier  each  morning  until  it  reaches  its 
farthest  point  west. 

As  it  starts  back  east  again  its  distance 
from  the  earth  increases  daily  until  it  reaches 
61 


THE    WAYS    OF    THE    PLANETS 

its  greatest  distance  from  us  at  superior 
conjunction.  It  is  then  the  whole  diameter 
of  its  orbit  farther  from  us  than  when  it  was 
at  inferior  conjunction,  and  it  is  again  in- 
visible. The  illuminated  side  of  it  is  tow- 
ard us ;  but  it  is  at  its  smallest,  because  it  is 
at  its  greatest  distance  from  us,  and  even 
when  it  is  not  directly  behind  the  sun  the 
light  of  that  luminary  is  too  great  for  suc- 
cessful competition.  After  it  has  passed  su- 
perior conjunction  it  is  again  in  the  evening 
sky,  apparently  moving  farther  from  the 
sun  each  day.  It  is  at  the  same  time  actu- 
ally coming  nearer  to  us  each  day,  and  these 
two  facts  cause  a  daily  increase  in  its  bright- 
ness. 

But  an  inferior  planet  is  not,  like  the  su- 
perior planets  and  the  stars,  brightest  when 
it  is  nearest  to  us.  It  is,  in  fact,  darkest  when 
it  is  nearest — that  is,  when  it  is  at  inferior 
conjunction — and  we  cannot  see  it  at  all. 
This  is  because  an  inferior  planet  passes 
through  phases,  like  the  moon,  changing 
gradually  during  its  rounds  from  full  to 
crescent,  and  back  again.  Its  full  face  is 
toward  us  when  it  is  on  the  opposite  side  of 
the  sun  and  farthest  from  us.  The  propor- 
tion of  the  face  that  is  illuminated  grows 
62 


INFERIOR  PLANETS:  SEEMING  MOTION 

smaller  as  the  planet  approaches  its  eastern 
elongation.  But  the  planet  grows  brighter 
because  it  is  coming  nearer  to  us  and  is 
getting  out  of  the  dazzling  rays  of  the  sun. 
One-half  of  its  surface  is  illuminated  when  it 
is  at  greatest  elongation;  but  it  is  brightest 
a  few  days  later,  when  less  than  half  of  its 
face  is  illuminated,  because  it  is  enough 
nearer  to  compensate  for  the  slight  diminu- 
tion in  the  proportion  of  light  on  its  disc. 
It  is  brightest  in  the  morning  a  short  time 
before  its  western  elongation,  for  the  same 
reason. 

This  in  a  general  way  describes  the  motion 
of  an  inferior  planet,  and  this  is  all  that  we 
need  to  know  in  order  to  understand  its 
ordinary  visible  movements.  If  we  watch 
it  carefully,  however,  we  may  detect  that 
shortly  before  inferior  conjunction  it  pauses 
in  its  onward  sweep  and  seems  for  a  time 
to  be  stationary,  and  then  to  retrace  its  way 
among  the  stars  until  a  short  time  after  in- 
ferior conjunction,  when  it  again  pauses 
and  appears  stationary,  and  finally  starts  off 
again  in  its  original  direction  on  its  way  tow- 
ard greatest  western  elongation.  During 
this  capricious  sort  of  progress  the  planet 
usually  describes  more  or  less  of  a  loop, 

63 


THE    WAYS    OF    THE    PLANETS 

sometimes  almost  a  flourish,  in  its  path. 
The  appearance  is  wholly  due  to  the  planet's 
overtaking  and  passing  us  in  our  journey 
around  the  sun.  For  a  time  it  travels  be- 
hind us,  then  beside  us,  and  then  beyond 
us;  and,  since  we  are  both  in  motion,  the 
effect  is  much  the  same  as  when  one  train 
passes  another  while  they  are  both  traveling 
in  the  same  direction.  The  orbits  of  the 
earth  and  the  planet  are  not  exactly  in  the 
same  plane,  and,  both  bodies  being  in  motion, 
we  are  not  in  a  position  to  see  the  planet  at 
the  same  angle  more  than  once  as  it  seems 
to  pass  back  and  forth,  and  so  we  get  the 
effect  of  its  making  a  flourish  or  loop.  But 
this  effect,  while  interesting,  takes  place  only 
when  the  planet  is  so  near  the  sun  that  to 
the  ordinary  observer  it  itself  does  not  count 
for  much.  We  can  see  but  little  of  the  in- 
ferior planets  at  that  time,  anyway,  though 
it  is  important  for  us  to  know  where  they 
are,  in  order  to  keep  track  of  them  and  to 
be  ready  for  them  when  they  are  to  be  seen. 


VIII 

HOW  THE  SUPERIOR  PLANETS  SEEM  TO  MOVE 

THE  movements  of  the  superior  planets, 
Mars,  Jupiter,  Saturn,  Uranus,  and 
Neptune,  as  they  appear  to  us,  are  different 
from  those  of  the  inferior  planets  in  some 
important  respects.  Instead  of  swinging 
back  and  forth  east  and  west  of  the  sun,  and 
never  appearing  very  far  away  from  it,  as 
the  inferior  planets  do,  the  superior  planets 
make  an  entire  circuit  of  the  heavens,  and 
it  is  possible  to  see  them  at  any  distance 
from  the  sun,  and  at  any  time  during  the 
night.  Sometimes  they  are,  with  relation 
to  the  earth,  in  that  part  of  the  sky  exactly 
opposite  to  the  sun,  and  hence  in  line  with 
it  and  the  earth.  At  such  times  they  can 
be  seen  all  night.  They  are  then  said  to  be 
in  opposition,  and  are  in  the  best  position 
for  our  observation.  The  earth  being,  when 
in  this  situation,  in  a  direct  line  between 
them  and  the  sun,  we  have  the  sun  at  our 
65 


THE    WAYS    OF    THE    PLANETS 

backs,  as  it  were,  shedding  its  full  rays  on 
the  disc  of  the  planet  under  observation, 
which  is  then  at  its  nearest  to  us,  and  also 
at  its  brightest.  For,  since  the  orbits  of  all 
the  superior  planets  are  outside  of  ours,  the 
planets  never  get  between  us  and  the  sun, 
and,  in  consequence,  never  turn  a  dark  side 
toward  us.  Their  entire  discs  are  practically 
always  illuminated,  and  their  changes  in 
brightness  depend  largely  upon  their  changes 
in  distance,  which,  as  we  have  seen,  is  not 
the  case  with  the  inferior  planets. 

Mars,  the  nearest  of  them,  is  at  times 
somewhat  gibbous  (that  is,  shows  a  little 
less  than  a  full  face,  as  the  moon  does  when 
just  beginning  to  wane),  and,  in  less  degree, 
Jupiter  also.  But  in  neither  case  is  this 
departure  from  fullness  sufficient  to  have 
any  appreciable  effect  on  the  planet 's  bright- 
ness, and,  moreover,  it  does  not  occur  when 
the  planet  is  in  the  most  favorable  position 
for  us  to  see  it.  At  opposition,  therefore, 
we  always  have  the  full  face  of  the  planet 
presented  to  us;  and  being,  as  we  then  are, 
on  the  same  side  of  the  sun  with  it,  we  are 
ninety-three  millions  of  miles  (our  distance 
from  the  sun)  nearer  to  it  than  the  sun  is. 

Being,  when  in  opposition,  exactly  oppo- 
66 


SUPERIOR  PLANETS:  SEEMING  MOTION 

site  the  sun,  the  planet  rises  just  as  the  sun 
sets.  After  opposition  it  rises  a  little  ear- 
lier each  evening,  and  is  higher  up  in  the  sky 
at  each  succeeding  sunset.  When  we  find  it 
just  half-way  between  the  eastern  and  the 
western  horizon  at  sunset,  it  is  at  quadra- 
ture. After  quadrature  it  appears  nearer 
and  nearer  the  western  horizon  each  evening 
at  sunset,  until  it  finally  is  too  near  the  sun 
to  be  visible.  It  is  then  traveling  in  that 
part  of  its  orbit  which  is  beyond  the  sun 
from  us.  From  opposition  to  this  situation 
it  has  been  an  evening  star. 

When  a  superior  planet  is  in  line  with  the 
sun  and  the  earth,  and  is  on  the  far  side  of 
the  sun  from  us,  it  is  said  to  be  in  con- 
junction, and  we  are  then  one  hundred  and 
eighty-six  millions  of  miles,  or  twice  our 
distance  from  the  sun,  farther  from  it  than 
we  are  when  it  is  in  opposition.  But  be- 
sides being  placed  at  so  much  greater  dis- 
tance from  it,  we  have  in  this  situation  the 
bright  sun  excluding  the  planet  from  our 
view.  It  will  be  readily  seen,  therefore,  why 
the  superior  planets  are  in  so  much  better 
position  for  us  to  see  them  in  opposition 
than  at  conjunction. 

From  conjunction  to  opposition  the  planet 
6  67 


THE    WAYS    OF    THE    PLANETS 

is  west  of  the  sun,  and  will  be  below  the 
horizon  at  sunset,  and  will  rise  some  time 
during  the  night.  At  first  it  will  appear 
just  before  sunrise  as  a  morning  star,  but 
will  gradually  rise  earlier  each  night  until, 
when  it  reaches  opposition  again,  it  will 
rise  just  as  the  sun  sets.  Half-way  between 
conjunction  and  opposition  it  is  again  at 
quadrature. 

From  opposition  to  conjunction  the  planet 
will  be  east  of  the  sun  and  above  the  horizon 
at  sunset.  When  a  planet  is  in  conjunction 
with  the  sun,  it  passes  the  meridian,  or  the 
point  half-way  between  rising  and  setting, 
about  noon,  and  is  above  the  horizon  with 
the  sun  during  the  day.  When  it  is  in  op- 
position it  passes  the  meridian  about  mid- 
night, and  is  above  the  horizon  during  the 
night.  When  it  is  at  quadrature  and  mov- 
ing toward  conjunction,  it  passes  the  merid- 
ian about  six  o'clock  in  the  evening,  and 
may  be  seen  in  the  western  half  of  the  sky 
during  the  early  evening,  and  will  set  before 
midnight.  When  it  is  at  quadrature  and 
moving  toward  opposition,  it  will  rise  some 
time  between  midnight  and  sunset,  and  will 
be  in  view  in  the  east  during  a  part  of  the 
first  half  of  the  night.  The  nearer  it  is  to 
68 


SUPERIOR  PLANETS:  SEEMING  MOTION 

opposition,  the  earlier  in  the  evening  it  rises 
and  the  longer  it  may  be  seen. 

The  main  movement  of  the  superior  planets 
among  the  stars  is  from  west  to  east,  and 
this  is  known  as  their  direct  motion.  But 
not  far  from  opposition  they  seem  to  hesi- 
tate, then  move  more  slowly,  then  finally 
stop,  remain  stationary  for  a  time,  turn 
back  on  their  tracks,  and  start  off  in  the 
opposite  direction.  This  is  their  retrograde 
motion.  They  do  not  continue  in  it  as 
long  as  in  the  direct  motion;  but  after  a 
comparatively  short  time  they  again  hesi- 
tate, go  more  slowly,  stop,  remain  station- 
ary, then  turn  back  and  swing  off  in  the 
original  direction,  and  continue  to  move  in 
this  direction  until  they  are  again  approaching 
opposition.  It  is  exactly  in  the  middle  of 
this  sweep  toward  the  west  that  the  planet 
is  in  opposition.  Close  observation  will 
show  that  the  superior  planets  also  make 
something  of  the  same  sort  of  a  loop  in  their 
path  among  the  stars  that  the  inferior  planets 
make,  and  for  the  same  reason.  The  only 
difference  is  that  when  a  superior  planet  is 
retrograding  we  are  passing  it,  and  when  an 
inferior  planet  retrogrades  it  is  passing  us. 

In  giving  this  rather  rough  outline  of  the 
69 


THE    WAYS    OF    THE    PLANETS 

way  the  planets  in  general  move  among  the 
stars,  reaching  in  their  wanderings  these 
various  positions  with  relation  to  the  sun 
and  the  earth,  the  intention  is  only  to  fix 
some  definite  situations  from  which  to  con- 
sider the  movements  of  the  individual 
planets.  When  we  come  to  know  each  planet 
as  an  individual,  and  to  follow  it  as  it  comes 
and  goes  in  the  heavens,  and  to  watch  its 
ever-wonderful  changes  in  brilliancy,  these 
situations  will  have  a  much  more  definite 
meaning  to  us  and  a  relatively  greater  in- 
terest and  importance.  The  planets  as  they 
appear  to  us  all  move  along  pretty  much  the 
ame  path;  but  each  has  its  own  way  of 
gracing  this  path,  and  each  its  particular 
manner  of  changing  in  aspect. 


IX 

THE   PATH    OF   THE    PLANETS 

THOUGH  the  planets  are  called  wan- 
derers, they  are  not  by  any  means  the 
vagrants  that  the  name  might  imply.  They 
have  a  fixed  course  among  the  stars  from 
which  they  never  deviate,  and  the  ways  of 
all  of  them,  arid  also  of  the  sun  and  the 
moon,  are  confined  to  a  comparatively  nar- 
row strip  in  the  sky. 

That  strip  is  called  the  zodiac.  Tt  is 
only  sixteen  degrees  wide,  and  extends  like  a 
narrow  band  all  the  way  around  the  heavens. 
It  lies  so  that  it  is  always  easy  to  observe; 
and,  being  so  limited,  very  little  observation 
is  necessary  to  become  familiar  with  every 
part  of  it.  Within  its  limits  all  the  move- 
ments of  the  sun,  the  moon,  and  the  planets 
take  place.  Through  the  center  of  it  is  the 
ecliptic,  the  great  circle  that  marks  the 
annual  apparent  path  of  the  sun  through 


THE    WAYS    OF    THE    PLANETS 

the  heavens.  It  is  the  standard  circle  from 
which  we  measure  the  paths  of  the  moon 
and  the  planets.  Whatever  degree  their 
courses  vary  from  the  ecliptic  is  what  we 
call  the  inclination  of  their  orbits.  If  the  plane 
of  the  orbit  of  a  planet  is  tilted  away  from  the 
ecliptic,  the  planet  will  travel  half  the  time 
on  one  side  of  it,  and  half  the  time  on  the 
other. 

The  orbits  are,  in  fact,  very  little  inclined 
to  the  ecliptic,  and  all  but  one  of  the  planets 
may  always  be  found  within  three  degrees 
of  it,  most  of  them  nearer  than  this.  The 
one  exception  is  Mercury,  which  is  sometimes 
much  as  seven  degrees  from  this  central 
line  of  the  zodiac,  but  ordinarily  it  is  not  so 
far  as  this.  Uranus  is  so  nearly  on  the 
ecliptic  that  an  ordinary  observer  would  not 
notice  the  deviation,  and  particularly  as 
Uranus  can  rarely  be  detected  with  the 
naked  eye,  and  can  never  be  thus  followed. 
Of  the  four  planets  which  are  the  ones  we 
ordinarily  see,  Mars  and  Jupiter  are  never 
as  much  as  two  degrees  from  the  ecliptic, 
Saturn  never  more  than  two  and  a  half 
degrees,  and  Venus  never  more  than  about 
three  degrees.  They  are  all  usually  nearer 
than  these  outside  limits.  The  greatest  dis- 
72 


THE    PATH    OF    THE    PLANETS 

tance  of  the  moon  from  the  ecliptic  is  about 
one  and  a  half  degrees. 

Hence,  with  the  exception  of  Mercury,  all 
the  planets  and  the  sun  and  the  moon  travel 
in  a  path  six  degrees  wide,  which  is  only  one 
degree  wider  than  the  distance  between  the 
pointers  as  we  see  them  in  the  Great  Dipper. 
The  fact  that  the  zodiac  is  sixteen  degrees 
wide,  or  eight  degrees  on  each  side  of  the 
ecliptic,  is  due  only  to  a  very  generous  al- 
lowance for  the  vagaries  of  Mercury,  which 
he  really  does  not  quite  need.  For  Mercury 
is  always  as  much  as  twice  the  breadth  of  the 
moon,  or  one  degree,  inside  of  the  zodiac,  and 
usually  more  than  that. 

Because  the  earth  is  tilted  on  its  axis 
twenty-three  and  a  half  degrees  from  the 
perpendicular,  the  ecliptic  runs  through  the 
heavens  in  an  oblique  circle,  crossing  the 
line  of  the  equator  at  two  points  called  the 
vernal  and  autumnal  equinoxes.  The  equa- 
tor in  the  heavens  is  the  great  circle  extend- 
ing around  the  celestial  sphere  half-way 
between  the  north  and  south  poles.  It  is 
always  practically  ninety  degrees  from  the 
north  star,  and  the  points  at  which  the 
ecliptic  intersects  it  are  called  the  equinoxes. 
These  are  the  only  two  points  on  the  ecliptic 
73 


THE    WAYS    OF    THE    PLANETS 

that  are  just  ninety  degrees  from  the  pole. 
The  word  equinox  is  derived  from  equus 
(equal)  and  nox  (night),  and  when  the  sun 
is  at  the  equinoxes  the  days  and  nights  are 
of  equal  length. 

From  the  vernal  to  the  autumnal  equinox 
the  line  of  the  ecliptic  is  north  of  the  equator, 
and  hence  high  in  the  sky,  reaching  its  high- 
est point  midway  between  the  equinoxes. 
It  then  crosses  the  equator  again  and  runs 
obliquely  south  to  the  lowest  point  in  its 
path,  and  then  curves  northerly  back  to  the 
vernal  equinox.  The  vernal  equinox  is  the 
point  at  which  the  sun  arrives  when  spring 
begins.  This  results  in  the  sun's  being 
\  north  of  the  equator  from  spring  until 
Autumn,  and  south  of  it  from  autumn  to 
spring. 

As  the  part  of  the  zodiac  that  we  can  see 
best  at  night  is  that  opposite  where  the  sun 
is,  so  in  summer,  when  the  sun  is  high,  we 
see  best  the  part  of  the  zodiac  which  is  low 
in  the  southern  skies  in  the  evening;  and  in 
the  winter,  when  the  sun  is  in  the  southern 
half  of  his  journey,  the  part  of  the  zodiac 
best  seen  by  us  is  high  in  the  heavens.  No 
part  of  it,  however,  is  ever  as  high  as  the 
zenith,  or  directly  overhead,  and  no  planet 
74 


THE    PATH    OF    THE    PLANETS 

is  ever  seen  as  far  north  as  the  zenith  in 
any  place  whose  latitude  is  more  than  twenty- 
three  and  one-half  degrees  from  the  equator. 

To  know  the  paths  of  the  planets  it  is 
necessary  to  know  only  twelve  constellations 
out  of  the  seventy  or  more  in  the  entire 
heavens;  but  it  is  difficult  to  imagine  any 
one's  learning  these  twelve  without  becom- 
ing interested  in  and  more  or  less  acquainted 
with  many  of  the  splendid  stars  and  con- 
stellations that  lie  on  each  side  of  them. 
The  larger  one's  acquaintance  is  with  the 
appearance  of  the  skies  as  a  whole,  the 
easier,  naturally,  it  will  be  to  distinguish 
the  planets  from  the  stars,  and  to  follow 
their  courses.  But  the  planets  themselves 
may  be  intimately  known  quite  apart  from 
any  but  the  twelve  constellations  forming 
the  zodiac.  Happily,  among  them  we  shall 
find  some  of  the  most  beautiful  constel- 
lations in  the  heavens,  and  some  of  the 
most  splendidly  brilliant  first  -  magnitude 
stars.1 

The  twelve  constellations  of  the  zodiac 
are  as  follows: 


1  The  reader  will  find  fuller  descriptions  of  the  stars  in  the 
zodiac  in  The  Friendly  Stars,  by  the  author  of  this  book. 

75 


THE    WAYS    OF    THE    PLANETS 

Pisces,  the  Fishes. 

Aries,  the  Ram. 

Taurus,  the  Bull. 

Gemini,  the  Twins. 

Cancer,  the  Crab. 

Leo,  the  Lion. 

Virgo,  the  Virgin. 

Libra,  the  Scales  or  Balance. 

Scorpio,  the  Scorpion. 

Sagittarius,  the  Archer. 

Capricornus,  the  Goat. 

Aquarius,  the  Water-Carrier. 

We  shall  begin  at  the  point  of  the  vernal 
equinox  to  trace  the  line  of  the  ecliptic 
through  these  constellations,  and  that  line 
will  mark  for  us  the  path  of  the  sun,  the  moon, 
and  all  the  planets.  It  is  convenient  to  be- 
gin at  this  point,  because  it  is  where  the  sun 
crosses  the  equator  in  the  spring,  and  hence 
it  is  at  the  beginning  of  that  part  of  the 
ecliptic  which  lies  north  of  the  equator. 

The  point  of  the  vernal  equinox  is  now 
situated  in  the  constellation  Pisces.  It  is 
not  marked  by  any  bright  star,  but  is  not 
very  difficult  to  find.  It  marks  the  point 
on  the  eastern  horizon  where  the  sun  rises 
about  March  2ist,  and  about  the  2ist  of 
September  it  is  on  the  eastern  horizon  exact- 
ly opposite  that  point  in  the  western  sky 
where  the  sun  sets.  It  is  always  ninety 

76 


76* 


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MAP    SHOWING    THE    CONSTELLATIONS    OF    THE    ZODIAC    A/ 
The  paths  of  all  the  planets,  save  one,  lie 


JO* 


VERNAL 

EQUINOX 


'HE    LINE    OF   THE    ECLIPTIC    RUNNING   THROUGH    THEM 

iays  within  three  degrees  of  the  ecliptic. 


THE    PATH    OF    THE    PLANETS 

degrees  from  the  pole,  and  if  one  chances 
to  know  the  constellation  Cassiopeia,  which 
is  shaped  like  a  chair  and  is  on  the  opposite 
side  of  the  pole  from  the  Big  Dipper,  one 
can  locate  the  vernal  equinox  by  drawing  a 
line  from  the  pole-star  through  the  star 
which  marks  the  lower  part  of  the  front  of 
the  chair,  and  extending  it  until  it  is  ninety 
degrees  long.  The  ninety  degrees  can  be  esti- 
mated by  using  the  distance  bet  ween  the  point- 
ers in  the  Dipper  (which  is  five  degrees)  as  a 
measure.  The  star  mentioned  in  Cassiopeia  is 
about  thirty-two  degrees  from  the  north  star. 
Having  once  learned  the  constellations  of 
the  zodiac  and,  approximately,  the  line  of 
the  ecliptic,  it  is  not  necessary  for  the  ordi- 
nary observer  to  keep  in  mind  the  exact 
location  of  the  vernal  equinox.  It  is,  how- 
ever, an  important  point  for  the  student  of 
mathematical  astronomy.  -...  -, 


Beginning  at  this  point,  the  ecliptic  runs 
through  Pisces  in  a  northeasterly  direction 
for  about  thirty  degrees  to  Aries,  the  second 
constellation  of  the  zodiac. 

ARIES 

Aries  is  best  seen  in  the  autumn  when  the 
sun  is  in  the  opposite  side  of  the  heavens.     It 
77 


THE    WAYS    OF    THE    PLANETS 

is  marked  by  a  small  acute-angled  triangle, 
with  the  apex  toward  the  north  and  the 
brightest  star  of  the  three  at  the  apex.  This 
star  is  called  Hamal,  and,  while  not  a  first- 
magnitude  star,  is  a  rather  bright  one  of  the 
second  magnitude;  and  the  triangle  itself  is 
very  distinctly  marked.  It  is  the  only 
group  of  stars  by  which  to  distinguish  Aries, 
and  it  is  sometimes  confused  with  the  little 
constellation  called  Triangulum,  which  lies 
just  west  of  it,  or  above  it,  as  it  rises.  With 
this  in  mind,  Triangulum  may  be  made  to 
serve  as  an  identifying  mark.  They  both 
rise  just  a  trifle  north  of  the  exact  east  early 
in  the  evenings  of  late  September  and  Octo- 
ber. Triangulum  rises  first,  with  its  apex 
toward  the  south.  In  less  than  an  hour  the 
triangle  of  Aries  arrives  with  its  apex  pointed 
north.  The  ecliptic  runs  about  five  degrees 
below  this  triangle,  and  its  path  across  Aries 
is  about  twenty-eight  degrees  long.  When 
one  sees  any  very  bright  star  in  Aries,  one 
may  be  sure  it  is  a  planet.  The  sun  is  in 
Aries  from  April  i6th  to  May  i3th. 

During  the  summer  this  constellation  is 

not  visible  in  the  early  evening;   but  it  may 

be  seen   every  evening  from  September  to 

April,  drawing  all  the  time  nearer  to  the  sun, 

78 


THE    PATH    OF    THE    PLANETS 

and  setting  earlier  each  evening  until  the 
sun  blots  it  out.  From  this  constellation 
the  ecliptic  runs  into  Taurus,  the  third 
zodiacal  constellation. 

TAURUS 

This  constellation  may  be  identified  by 
the  brilliant  first  -  magnitude  star  Alde- 
baran,1  and  the  misty  Little  Dipper  of  the 
Pleiades.  It  is  a  very  beautiful  and  large 
constellation.  About  an  hour  and  a  half 
after  the  triangle  of  Aries  has  risen,  the  soft- 
twinkling  cluster  of  tiny  stars  which  form 
the  Pleiades  comes  above  the  eastern  hori- 
zon, and  about  an  hour  later  a  V-shaped 
cluster  of  brighter  stars,  with  a  very  bright- 
red  one  at  the  end  of  the  lower  half  of  the 
V,  appears.  This  last  cluster  is  the  Hyades, 
and  the  bright  star  is  Aldebaran. 

By  these  two  clusters  we  may  know  the 
constellation.  The  ecliptic  passes  across 
Taurus  about  four  degrees  east  of  the 
Pleiades,  and  about  seven  degrees  west  of 
Aldebaran.  The  planets  in  passing  through 
this  region  often  come  very  close  to  the 

JSee  "Aldebaran"  in  The  Friendly  Stars. 
79 


THE    WAYS    OF    THE    PLANETS 

Pleiades,  and  parts  of  the  group  are  some- 
times occulted  by  the  moon.  Taurus  is 
conspicuous  in  the  eastern  evening  sky  from 
September  until  nearly  January.  From  that 
time  on  until  May  it  may  be  seen  in  the 
evening,  high  up  in  the  sky,  a  little  farther 
west  each  evening,  until  it  disappears  in 
May.  Among  the  four  planets  that  we  most 
see  Mars  is  the  only  one  a  that  resembles 
Aldebaran  in  color.  They  are  both  reddish, 
but  Mars  is  always  west  of  Aldebaran  near 
the  line  of  the  ecliptic,  and  also  it  does  not 
have  the  same  twinkling  face  that  Alde- 
baran shows;  hence  the  star  and  the  planet 
need  never  be  confused.  Mercury,  it  is 
true,  is  reddish  and  twinkles,  but  so  seldom 
needs  to  be  taken  into  account  that  it  will 
not  be  troublesome.  The  other  planets  when 
in  Taurus  will  proclaim  themselves  by  their 
color  and  size.  There  is  no  very  bright  star 
in  Taurus  except  Aldebaran,  which  has  been 
described.  Any  bright  star  north  of  it  in 
the  constellation  is  sure  to  be  a  planet. 

Through  Taurus  the  line  of  the  ecliptic 
runs  in  a  northeasterly  direction,  and  about 
fifteen  degrees  east  from  Aldebaran  it  passes 
about  half-way  between  two  fairly  bright 
£tars  which  mark  the  tips  of  the  horns  of 
80 


THE    PATH    OF    THE    PLANETS 

Taurus,  and  from  there  on  into  the  fourth 
constellation. 

GEMINI 

Gemini  lies  northeast  of  Taurus,  and  is 
outlined  by  a  box- shaped  figure  something 
more  than  twenty  degrees  long  and  about 
five  degrees  wide.  The  two  stars  marking 
the  end  of  it  farthest  from  Taurus  are  the 
famous  twins,  Castor  and  Pollux.1  Pollux 
is  a  first-magnitude  star,  and  Castor  is  very 
little  less  bright.  They  are  both  very  charm- 
ing stars,  and  too  conspicuous  to  escape  easy 
identification.  Castor  is  greenish  in  tint, 
and  rises  between  an  hour  and  a  half  and 
two  hours  later  than  Aldebaran.  About 
fifteen  minutes  after  he  appears,  Pollux, 
with  a  yellow-tinted  face,  comes  up  over 
the  eastern  horizon.  They  rise  about  thirty 
degrees  north  of  the  exact  east.  The  eclip- 
tic has  reached  its  highest  point  north  just 
after  passing  through  the  horns  of  Taurus. 
It  then  runs  through  Gemini  in  a  south- 
easterly direction,  curving  diagonally  across 
the  main  figure  and  passing  five  or  six  de- 
grees below  Pollux.  Gemini  can  be  seen 

1See  "The  Heavenly  Twins"  in  The  Friendly  Stars. 
81 


THE    WAYS    OF    THE    PLANETS 

from  October  to  early  June.  It  is  particu- 
larly charming  in  May  in  the  northwest 
just  after  sundown,  and  when  any  of  the 
planets  are  going  along  this  part  of  their 
path  at  that  season,  they  are  sure  to  win 
one's  interest  and  admiration. 

CANCER 

After  leaving  Gemini  the  ecliptic  passes 
through  the  small  constellation  Cancer.  Its 
way  runs  southeasterly  for  about  twenty 
degrees,  passing  just  south  of  a  charming 
little  cluster  of  stars  which  can  be  dimly 
seen  with  the  unaided  eye,  but  comes  out 
brilliantly  with  an  opera-glass.  It  is  called 
Praesepe,  or  the  Bee-hive,  and  is  the  only 
object  to  attract  attention  in  Cancer.  For- 
tunately, it  is  so)  situated  as  to  mark  the 
line  of  the  ecliptic  through  the  constellation. 
The  Bee-hive  rests  almost  exactly  on  the 
ecliptic. 

LEO 

Leaving  Cancer,   the  sun  enters  Leo,  a 

large,   well-marked  constellation  known  to 

many  persons  by  the  conspicuous  figure  in 

it  of  a  sickle.     At  the  end  of  the  handle  of 

82 


THE    PATH    OF    THE    PLANETS 

the  Sickle  is  Regulus,  one  of  the  bright  first  - 
magnitude  stars.  A  little  more  than  fifteen 
degrees  east  of  the  Sickle  the  rest  of  the  con- 
stellation is  marked  by  a  large  triangle 
formed  by  three  rather  bright  stars.  Both 
of  these  figures  are  well  marked  and  easily 
seen,  making  Leo  one  of  the  easiest  of  the 
constellations  to  find.  The  sun  crosses  it  in 
a  southeasterly  direction  which  leads  straight 
across  Regulus.  The  star  is  often  occulted 
by  the  moon,  and  by  the  sun  also,  though 
that  we  cannot  see  on  account  of  the  blind- 
ing light  of  the  sun. 

Leo  is  visible  nearly  eight  months  in  the 
year.  It  is  in  the  eastern  sky  early  in  the 
evening  in  the  winter,  and  shines  all  night 
from  late  in  December  until  April.  In  May 
and  June  it  is  traveling  westerly,  but  high 
up  in  the  sky.  In  July  it  is  in  the  western 
sky  in  the  evening.  The  sun  passes  through 
it  from  August  7th  to  September  i4th. 
Regulus  is  a  white  star,  and  twinkles  violent- 
ly, so  that  it  is  easily  distinguished  from  any 
planet  that  is  passing  near  it.  In  the  other 
part  of  the  constellation  the  path  of  the 
planets  runs  about  ten  degrees  below  the 
triangle. 

7  83 


THE    WAYS    OF    THE    PLANETS 
VIRGO 

When  the  sun  has  passed  Leo  it  enters  the 
largest  of  all  the  constellations,  Virgo,  and 
passes  through  it  in  forty-five  days,  from 
September  i4th  to  October  2pth.  The  con- 
stellation is  far  from  rich  in  bright  stars; 
but  one  may  find  the  ecliptic,  or  path  of  the 
sun,  by  following  a  curved  southeasterly  line 
from  Regulus  about  sixty-five  degrees  until 
it  reaches  Spica,1  a  very  bright  first-magni- 
tude star  in  this  comparatively  starless 
region.  If  there  is  any  doubt  about  Spica, 
it  may  be  found  by  following  the  curve  of  the 
handle  of  the  Big  Dipper  about  thirty  de- 
grees, which  brings  one  to  the  splendid 
Arcturus,  and  then  about  thirty  degrees 
farther  on,  which  points  one  to  Spica. 

Eight  or  nine  days  after  entering  Virgo 
the  sun  crosses  the  equator  at  the  autumnal 
equinox,  and  the  rest  of  the  ecliptic  lies 
farther  south.  Spica  is  about  ten  degrees 
south  of  the  equator. 

Spica  is  in  the  east  during  the  early  eve- 
nings in  April  and  May;  throughout  June 
and  July  it  may  be  seen  in  the  south  during 


Spica"  in  The  Friendly  Stars. 
84 


THE    PATH    OF    THE    PLANETS 

the  evening.     In  October  it  sets  at  about 
the  same  time  as  the  sun. 

The  autumnal  equinox,  or  the  point  where 
the  ecliptic  crosses  to  the  south  of  the 
equator,  is  in  Virgo,  and  lies  about  fifteen 
degrees  northeast  of  Spica. 

LIBRA 

Libra  is  the  next  zodiacal  constellation, 
and  it  is  a  small  one.  The  sun  passes  through 
it  in  about  twenty-three  days.  It  may  be 
known  by  four  fairly  bright  stars  which  form 
a  more  or  less  imperfect  square.  The  ecliptic 
passes  along  the  southern  edge  of  this  figure. 

During  the  summer  and  early  autumn, 
Libra  is  best  seen.  It  is  then  passing  across 
the  southern  sky,  drawing  nearer  the  west 
each  evening.  A  planet  passing  across  this 
constellation  would  always  be  easy  to  identi- 
fy, since  it  would  always  be  so  much  brighter 
than  any  star  in  this  region.  The  sun  enters 
Libra  about  October  2gth,  and  it  is  not  vis- 
ible in  the  evening  during  the  rest  of  the 
year. 

SCORPIO 

It  is  a  joy  to  know  Scorpio,  quite  aside 
from  its  connection  with  the  path  of  the 
85 


THE   WAYS    OF    THE    PLANETS 

planets.  It  is  a  brilliant  constellation,  best 
seen  during  the  summer  and  autumn,  as  it 
passes  across  the  southern  sky.  It  is  the 
most  southerly  of  any  of  the  constellations  of 
the  zodiac;  but  the  ecliptic  passes  through 
only  a  very  small  portion  of  the  northern 
part  of  it,  so  the  sun  does  not  reach  the 
most  southerly  point  in  its  path  while  it  is 
in  this  constellation. 

Scorpio  may  be  best  identified  by  its  bril- 
liant deep-red  star  Ant  ares,1  which  is  sup- 
posed to  lie  in  the  heart  of  the  Scorpion. 
The  whole  figure  makes  a  splendid  ser- 
pent-like sweep  toward  the  southern  horizon, 
and  is  one  of  the  most  conspicuous  ob- 
jects just  west  of  the  Milky  Way  in  the 
south  in  summer. 

The  line  of  the  ecliptic  runs  about  three 
degrees  north  of  Antares;  hence  the  planets 
in  their  course  sometimes  pass  very  near  it. 
Jupiter  has  been  in  that  region  all  this  year 
(1912),  and  will  not  be  far  from  there  the 
early  part  of  1913.  Mercury  and  Mars 
both  have  something  the  color  of  Antares; 
but  this  is  not  likely  to  result  in  any  con- 
fusion. The  star  is  always  there,  and  in  the 

1  See  "Antares"  in  The  Friendly  Stars. 
86 


THE    PATH    OF    THE    PLANETS 

same  relative  situation  with  reference  to  the 
other  stars.  When  Mars  is  there,  it  will 
always  be  above  the  star.  Mercury  can  sel- 
dom be  seen  when  he  is  in  Scorpio.  If  he  is 
in  greatest  elongation  while  there,  he  will  still 
be  near  the  sun,  and  the  sun,  as  seen  from  the 
middle  latitudes,  is  so  far  south  and  so  near 
the  horizon  when  in  that  part  of  the  ecliptic 
that  the  situation  will  not  be  favorable  for 
seeing  the  planet.  Farther  south,  and  par- 
ticularly in  high  altitudes,  Mercury  could 
be  well  seen  in  Scorpio,  but  if  the  position 
of  Antares  is  kept  in  mind,  Mercury  will 
easily  be  recognized  as  a  stranger  in  the 
constellation. 

The  sun  enters  Scorpio  about  November 
2ist,  and  the  constellation  then  ceases  to 
be  visible  in  the  evening  sky  until  the  fol- 
lowing May.  It  is  in  its  greatest  glory 
during  the  summer  and  early  autumn. 

SAGITTARIUS 

When  the  sun  leaves  Scorpio  it  crosses 
the  Milky  Way  into  Sagittarius,  and  there 
reaches  the  lowest  point  in  its  path,  twenty- 
three  and  one-half  degrees  south  of  the 
equator.  This  constellation  is  best  dis- 
87 


THE    WAYS    OF    THE    PLANETS 

tinguished  by  the  little  "milk  dipper,"  which 
is  easily  seen  turned  upside  down  just  at  the 
eastern  edge  of  the  Milky  Way.  The  line 
of  the  ecliptic  runs  a  little  north  of  it.  The 
constellation  may  be  best  seen  during  about 
the  same  months  that  Scorpio  is  visible. 
The  sun  enters  it,  and  it  passes  out  of  view 
about  the  middle  of  December. 

CAPRICORNUS  AND  AQUARIUS 

From  Sagittarius  the  ecliptic  runs  in  a 
northeasterly  direction  through  a  region  in 
which  there  are  no  very  bright  stars,  nor 
any  very  distinct  outlines  of  figures.  The 
two  constellations  through  which  it  passes 
are  Capricornus  and  Aquarius.  It  then  runs 
a  few  degrees  into  Pisces,  and  there  reaches 
the  vernal  equinox,  where  we  began  to  trace 
its  course. 

Although  one  cannot  trace  the  line  of  the 
ecliptic  with  the  same  defmiteness  in  this 
region  as  in  one  where  there  are  bright  stars 
to  mark  the  way,  yet  when  a  planet  is  in 
this  part  of  its  path  it  is  perhaps  more  con- 
spicuous and  more  easily  recognized  than 
when  it  appears  in  any  other  part  of  the  sky, 
because  of  the  very  absence  of  other  bright 
88 


THE    PATH    OF    THE    PLANETS 

bodies.  These  constellations  comprise  all  that 
region  running  from  the  Milky  Way  east 
to  the  vernal  equinox.  It  is  a  part  of  the 
heavens  easily  seen  during  the  pleasant 
evenings  of  summer  and  autumn,  and  if  a 
planet  is  crossing  it  during  those  seasons  it 
is  particularly  well  placed  for  observation. 

The  two  brightest  stars  in  Capricornus 
are  of  the  third  magnitude,  and  lie  about 
twenty  degrees  northeast  of  the  "milk  dip- 
per." The  ecliptic  runs  just  under  them. 
Through  Aquarius  it  runs  six  or  seven  de- 
grees above  a  waving  line  of  faint  stars, 
which  are  supposed  to  represent  the  water 
that  Aquarius  is  pouring  from  his  urn. 

If  one  will  take  the  trouble  to  trace  the 
line  of  the  ecliptic  through  the  sky,  and  re- 
member that  it  lies  exactly  in  the  center  of 
the  zodiac,  and  that  the  planets  are,  there- 
fore, within  a  very  few  degrees  of  it,  one  will 
have  no  trouble  in  keeping  track  of  them. 
The  mere  knowing  of  these  constellations  is 
in  most  cases  sufficient,  since  the  planets  will 
disclose  their  identity  in  other  ways  than  by 
position  merely. 

The  signs  of  the  zodiac  are  somewhat  dif- 
ferent from  the  constellations.  They  are 
simply  twelve  equal  divisions  of  thirty  de- 


THE    WAYS    OF    THE    PLANETS 

grees  each,  making  in  all  three  hundred  and 
sixty  degrees,  which  is  the  whole  number  of 
degrees  in  any  circle.  They  are  so  divided 
for  convenience  in  scientific  observation  and 
reckoning.  About  two  thousand  years  ago 
the  signs  and  the  constellations  in  the  main 
coincided,  and  they  still  bear  the  same  names. 
The  point  of  the  vernal  equinox  was  then  at 
the  beginning  of  the  sign  and  the  constella- 
tion Aries.  But,  owing  to  certain  motions 
of  the  earth,  this  point  shifts  backward,  or 
toward  the  west,  about  one  degree  e very- 
seventy- two  years.  In  two  thousand  years 
it  has  shifted  about  twenty-eight  degrees, 
until  now  the  sign  Aries,  with  the  vernal 
equinox  at  its  western  boundary,  lies  almost 
wholly  in  the  constellation  Pisces,  the  sign 
Taurus  corresponds  approximately  to  the 
constellation  Aries,  and  so  on  around  the 
circle.  It  is  important  to  know  this  in  fol- 
lowing the  planets,  because  all  almanacs  and 
scientific  publications  deal  mainly  with  the 
signs  of  the  zodiac,  and  not  with  the  constella- 
tions. When  a  planet's  place  is  said  to  be 
in  Aries,  Taurus,  or  Gemini,  one  will  find  it  in 
Pisces,  Aries,  or  Taurus,  respectively.  And 
so  it  is  with  all  the  other  signs;  they  are 
each  one  constellation  behind  the  one  bear- 
90 


THE    PATH    OF    THE    PLANETS 


ing  the  same  name.  And  this  is  why,  be- 
ginning with  the  vernal  equinox,  Pisces  is 
the  first  constellation  in  the  zodiac,  while 
Aries  is  the  first  sign. 

The  following  is  a  list  of  the  signs  of  the 
zodiac,  with  the  corresponding  constella- 
tions. The  symbols  given  in  parenthesis 
are  the  ones  used  for  these  signs  in  all 
almanacs : 

CONSTELLATION 

Pisces 

Aries 

Taurus 

Gemini 
Cancer 
Leo 

Virgo 
Libra 
Scorpio 

Sagittarius 

Capricornus 

Aquarius1 

1  For  those  who  find  rhymes  an  aid  to  memory,  the  fol- 
lowing list  may  prove  useful : 

This  is  the  way  the  spring  begins: 
First  Aries,  then  Taurus,  then  the  Heavenly  Twins. 
The  first  summer  sign  is  the  one  we  call  Cancer; 
The  next  two  to  Leo  and  Virgo  will  answer. 
Then  autumn  brings  Libra  and  bright  Scorpio, 

91 


SIGN 

Spring 

(  Aries 
<  Taurus 
(  Gemini 

(f) 

8 

(n) 

Summer 
signs 

(  Cancer 
]Leo 
(  Virgo 

(0 
(SI 
(HB 

Autumn 

(  Libra 
•j  Scorpio  y 
(  Sagittarius 

if 

Winter 

(  Capricornus 
<  Aquarius 
(  Pisces 

(vs; 

83 

THE    WAYS    OF    THE    PLANETS 

And  next  Sagittarius,  with  his  strong  bow. 

Capricornus  then  ushers  the  winter  in, 

And  near  old  Aquarius  the  year  we  begin. 

Pisces  comes  next,  and  then  winter  is  done; 

And  with  Aries's  approach,  a  new  spring  is  begun. 

These  are  the  signs;    but  bear  this  well  in  mind: 

The  sun  lags  in  one  constellation  behind. 

When  his  place  is  Aries,  we'll  find  him  in  Pisces; 

When  in  Taurus  he  should  be,  in  Aries  he  stays. 

If  Gemini's  his  place,  and  to  find  him  our  wish  is, 

We  must  look  back  in  Taurus  to  see  his  bright  rays. 

And  so  through  the  year,  whatever  his  place  is, 

The  bright  group  behind  is  the  one  that  he  graces. 


X 

MERCURY 

WHILE  Mercury  is  one  of  the  five  planets 
that  can  be  seen  with  the  naked  eye, 
it  must  be  confessed  that  he  does  not  play 
any  important  part  in  the  great  spectacle 
of  nature  as  we  see  it  in  the  skies.  But  in 
a  certain  way  this  only  adds  to  our  interest 
in  him.  The  very  rarity  of  his  appearances 
and  the  difficulty  of  finding  him  give  a  zest 
to  the  search,  and  a  sense  of  achievement, 
when  it  is  successful,  that  one  does  not  have 
with  regard  to  the  other  planets.  It  is 
something  akin  to  the  feeling  one  has  when, 
after  a  long  tramp  to  some  secluded  recess 
in  the  woods  in  search  of  the  shy  pink  lady's 
slipper,  a  splendid  specimen  of  that  lovely 
flower  suddenly  comes  into  view  hanging 
gaily  on  its  stalk,  ready  for  the  use  of  what- 
ever fairy  foot  may  tread  its  shady  groves. 

Then,  too,  the  spring  o'  the  year  is  the  most 
likely  time  to  see  Mercury  in  the  evening  sky. 
He  comes  into  his  best  position  for  this  view 
93 


THE    WAYS    OF    THE    PLANETS 

of  him  just  when  the  evenings  are  growing 
longer  and  milder  and  one  begins  to  hunger 
for  outdoor  things,  so  that  the  quest  of 
him  at  that  time  has  the  gladness  that  goes 
with  our  first  excursions  into  the  open  after 
a  winter's  housing,  whether  it  be  in  search  of 
flowers,  or  birds,  or  stars,  or  simply  the  gen- 
eral loveliness  of  everything  that  belongs  to 
the  beginning  of  the  outdoor  season. 

The  reason  Mercury  is  so  elusive  is  that 
he  is  always  very  near  the  sun,  and  in  con- 
sequence his  light  is  dimmed  by  the  brighter 
light  shed  by  that  luminary  until  it  is  well 
below  the  horizon;  and  after  the  sun  has 
set,  the  planet  is  so  involved  in  the  usual 
haziness  of  the  atmosphere  near  the  hori- 
zon that  the  conditions  must  be  very  favor- 
able in  order  to  see  him.  Though  there  are 
recorded  observations  of  Mercury  as  far 
back  as  nearly  three  hundred  years  before 
Christ,  yet  some  of  the  older  of  the  modern 
astronomers,  before  the  days  of  the  perfected 
telescope,  are  said  not  to  have  seen  him  at 
all;  and  the  most  important  observations  of 
the  planet  nowadays  are  made  in  broad  day- 
light, when  it  is  higher  up  in  the  skies  and 
free  from  the  mists  of  the  horizon.  This 
can  be  done  by  means  of  a  powerful  tele- 
94 


MERCURY 

scope,  because  it  is  possible  in  this  way  to 
shut  off  the  light  of  surrounding  bodies; 
but,  of  course,  the  conditions  are  not  as 
favorable  as  if  midnight  observations  could 
be  made.  Still,  if  one  knows  just  when  and 
where  to  look,  Mercury  can  be  seen  with 
the  naked  eye  at  least  once  or  twice  a  year, 
and  sometimes  oftener  than  this,  especially 
if  one  chances  to  live  in  one  of  the  Western 
States,  where  the  air  is  very  clear  and  the 
situation  in  latitude  and  altitude  more  fa- 
vorable than,  say,  in  New  England,  or  in  the 
middle  Atlantic  States.  In  our  Northern 
States,  and  in  the  whole  of  England,  this 
planet  is  more  difficult  to  see,  because  of 
the  longer  twilight  in  northern  latitudes, 
and  also  because  the  line  of  the  ecliptic,  over 
which  it  passes,  seems  there  lower  down  in 
the  skies,  while  in  the  far  South,  say  in 
Cuba  or  Porto  Rico,  the  twilight  is  shorter, 
the  ecliptic  runs  high  in  the  sky,  and  the 
situation  is  favorable  for  a  good  view  even 
though  the  atmosphere  is  no  clearer  than 
it  is  farther  north. 

WHEN  AND  WHERE   TO   FIND   MERCURY 

Mercury    is    never    more    than    twenty- 
eight  degrees  from  the  sun,  and  is  bright- 
95 


THE    WAYS    OF    THE    PLANETS 

est  when  the  distance  between  them  is 
somewhere  near  twenty  -  two  degrees,  or 
about  four  times  the  distance  between  the 
pointers  in  the  Big  Dipper.  The  direction 
in  which  to  search  for  him  must  always  be 
along  the  line  of  the  ecliptic  obliquely  above 
the  sun.  Since  his  orbit  is  inclined  seven 
degrees  to  the  ecliptic,  he  will  be  some  place 
within  seven  degrees  of  this  line,  on  one  side 
or  the  other.  Within  this  narrow  strip  in 
the  sky,  fourteen  degrees  wide  and  twenty- 
eight  degrees  long,  Mercury  will  be  found 
whenever  he  is  visible  at  all.  And  this  strip 
may  be  further  shortened  by  at  least  twelve 
degrees;  for  when  the  planet  is  nearer  than 
that  to  the  sun  it  is  futile  to  attempt  to  see 
him  with  the  naked  eye,  save  in  very  ex- 
ceptional conditions.  The  five  degrees  be- 
tween the  pointers  will  serve  as  an  aid  in 
measuring  these  distances. 

We  can  never  see  Mercury  with  the  naked 
eye  except  when  he  is  near  one  elongation  or 
the  other;  and  even  then  he  is  visible  only 
about  an  hour  after  the  sun  is  down  in  the 
evening  or  about  an  hour  before  it  rises  in 
the  morning.  Three  times  each  year  he 
appears  in  the  evening  for  more  or  less  than 
a  week,  according  to  the  situation  of  the 
96 


MERCURY 

observer,  and  three  times  a  year  he  is  visible 
in  the  morning  for  about  the  same  length  of 
time.  But,  owing  to  his  position  with  rela- 
tion to  us,  the  evening  exhibit  that  comes  in 
the  spring  is  the  most  favorable  one  for  a 
good  view  of  him,  and  the  morning  appear- 
ance that  is  most  favorable  is  the  one  that 
comes  in  the  autumn. 

The  mean  synodic  period  of  Mercury  is 
about  one  hundred  and  sixteen  days,  or  a 
little  less  than  four  months.  That  is,  he 
returns  to  greatest  eastern  elongation  and 
can  be  seen  in  the  evening  sky  about  every 
one  hundred  and  sixteen  days,  and  the  same 
length  of  time  elapses  between  his  appear- 
ances in  the  morning  sky  at  greatest  western 
elongation.  But  this  mean  synodic  period 
is  made  up  of  synodic  periods  varying  in  dif- 
ferent revolutions  from  one  hundred  and  five 
to  one  hundred  and  thirty-four  days.  So, 
though  one  may  mark  the  dates  at  which  the 
various  positions  of  the  planet  occurred  dur- 
ing any  one  revolution,  one  cannot  so  easily 
determine  the  exact  time  at  which  he  will 
be  found  in  the  same  positions  at  the  next 
revolution;  that  is,  whether  the  revolution 
will  take  place  in  less  or  more  than  one  hun- 
dred and  sixteen  days.  The  earth  and  the 
97 


THE    WAYS    OF    THE    PLANETS 

planet  are  each  traveling  at  varying  rates 
of  speed,  according  as  they  are  near  the  sun 
or  farther  from  it,  and  obviously  it  is  a  situa- 
tion that  requires  careful  mathematical  work 
to  compute.  The  almanac  must  be  referred 
to  for  the  exact  date. 

But,  lacking  an  almanac,  one  will  generally 
find  that  Mercury  will  return  to  the  same 
position  relative  to  the  earth  and  the  sun 
within  a  few  days  of  his  mean  synodic  period. 
Three  periods,  however  much  they  may  vary 
individually,  are  almost  always  equal  to 
three  hundred  and  forty-eight  days,  or  three 
times  the  mean  period.  This  is  seventeen 
days  less  than  a  year.  Hence,  if  one  is 
lucky  enough  to  have  seen  Mercury  at  east- 
ern elongation  one  spring,  and  will  look  the 
next  year  about  seventeen  days  earlier,  the 
planet  will  be  found  a  little  to  the  east 
(about  fifteen  degrees)  of  where  he  was  when 
first  seen  the  year  before.  He  is  there  in 
the  same  position  with  relation  to  us  and 
the  sun  that  he  had  the  preceding  spring, 
but  in  a  slightly  different  relation  to  us  and 
the  stars,  because  the  sun  lacks  seventeen 
days  of  having  completed  its  apparent  year- 
ly journey  around  the  zodiac.  It  must  still 
go  through  about  one  half  of  a  constellation. 
98 


MERCURY 

When  Mercury  shows  himself  at  eastern 
elongation,  he  may  be  seen  in  the  west  as 
an  evening  star  for  somewhere  near  a  week, 
each  evening  drawing  nearer  to  the  sun. 
When  he  disappears  from  view  he  passes  be- 
tween us  and  the  sun,  and  about  four  weeks 
later  appears  in  the  morning  sky  before  the 
sun  rises.  Under  favorable  conditions  he  is 
again  visible  for  a  week  or  more;  and  then, 
again  approaching  the  sun,  he  can  be  seen 
no  more  for  about  ten  weeks,  during  which 
time  he  passes  through  superior  conjunction 
on  the  other  side  of  the  sun  from  us  and 
comes  back  to  eastern  elongation. 

Thus  we  can  get,  under  very  favorable 
conditions,  six  short  views  of  Mercury  dur- 
ing the  year — three  in  the  evening  and  three 
in  the  morning.  So  many  views,  however, 
are  rarely  secured  by  any  but  the  professional 
observer.  The  circumstances  may  well  be 
considered  felicitous  if  one  succeeds  in  get- 
ting a  glimpse  of  him  once  or  twice  a  year — 
at  his  favorable  situation  in  the  evening  in 
the  spring  and  the  morning  in  the  autumn. 
The  sight  of  him,  though,  is  truly  worth  a 
little  inconvenience — even  to  the  extent  of 
facing  a  cold  evening  wind  in  the  very  early 
spring  or  getting  out  of  a  comfortable  bed 
8  99 


THE   WAYS    OF    THE    PLANETS 

before  dawn  during  the  first  cool  mornings 
of  autumn. 

It  is  hardly  possible  to  say  exactly  where 
one  can  find  Mercury  at  all  times  during 
a  long  succession  of  revolutions.  Moreover, 
it  is  not  necessary.  These  computations 
are  made  anew  each  year  by  experts  in  the 
employ  of  the  government,  and  the  result 
is  published  in  the  Nautical  Almanac.  From 
there  it  finds  its  way  into  all  almanacs,  so 
it  is  easy  of  access  to  any  one. 

In  the  almanacs  Mercury  is  represented 
by  the  sign  (S).  It  is  a  conventionalized 
form  of  the  caduceus,  or  wand,  carried  by 
the  god  Mercury  as  a  symbol  of  his  power. 

The  next  seven  eastern  and  western  elon- 
gations of  Mercury  occurring  after  the  pub- 
lication of  this  book  are  as  follows: 

Eastern  Elongation  Western  Elongation 

(Evening  Star).  (Morning  Star). 

18  November,  1912.  27  December,  1912. 

10  March,  1913.  24  April,  1913. 

(Favorable  for  viewing.) 
7  July,  1913  22  August,  1913. 

(Favorable  for  viewing.) 
i  November,  1913.  10  December,  1913. 

22  February,  1914.  6  April,  1914. 

(Favorable  for  viewing.) 
18  June,  1914.  5  August,  1914. 

(Favorable  for  viewing.) 
15  October,  1914.  23  November,  1914. 

100 


MERCURY,,;  A;,,    iJ 
DISTANCE   AND   BRIGHTNESS 

Of  all  the  planets  Mercury  is  nearest  the 
sun.  His  average  distance  is  thirty-six 
million  miles.  He  is  nearly  eighty  times 
nearer  than  Neptune,  the  outermost  planet, 
and  more  than  two  and  one-half  times  nearer 
than  we  are.  But  his  orbit  departs  so  far 
from  being  a  circle  that  his  distance  from 
the  sun  varies  as  much  as  fifteen  million 
miles.  When  he  is  nearest  the  sun,  or  in 
perihelion,  he  is  only  twenty-eight  million 
miles  from  it;  when  he  is  farthest,  or  in 
aphelion,  his  distance  is  forty-three  million 
miles.  There  is  even  greater  variation  in  his 
distance  from  us.  The  difference  between 
his  least  possible  and  his  greatest  possible 
distance  from  us  is  as  much  as  eighty-nine 
millions  of  miles.  For  the  earth  has  an 
elliptical  orbit  as  well  as  Mercury,  and  when 
we  are  at  perihelion,  which  occurs  in  the 
winter,  we  are  three  millions  of  miles  nearer 
to  the  sun  than  we  are  in  mid-summer.  If 
Mercury  chances  to  be  then  at  his  greatest 
distance  from  the  sun,  and  also  at  inferior 
conjunction,  or  between  us  and  the  sun,  he 
is  only  forty-seven  millions  of  miles  from  us. 
If,  when  we  are  farthest  from  the  sun,  he 
101 


THE  AVAYS    OF    THE    PLANETS 

also  is  at  his  greatest  distance  from  it,  and 
is  in  superior  conjunction,  or  on  the  other 
side  of  the  sun  from  us,  he  is  one  hundred 
and  thirty-six  millions  of  miles  from  us. 

These  changes  in  distance  from  the  earth 
have  much  to  do  with  Mercury's  changes 
in  apparent  brightness  to  us.  At  his  bright- 
est, when  he  appears  at  greatest  elongation 
and  we  can  see  him  without  a  telescope,  he 
is  brighter  than  Arcturus,  the  brilliant  first- 
magnitude  star  in  Bootes,  that  swings  over 
us  nightly  from  early  spring  to  late  autumn. 
When  seen  with  the  naked  eye,  he  is  also 
red  in  color,  somewhat  like  Arcturus;  but 
through  a  telescope  he  is  dull  silver,  like  the 
moon,  or  even  more  ashy  in  his  paleness. 
As  he  goes  farther  and  farther  from  us  he 
becomes  dimmer  and  dimmer  and  can  be 
followed  only  with  a  telescope  until,  even 
with  this  aid  to  vision,  he  is  lost  in  the  rays 
of  the  sun  at  superior  conjunction.  His  ap- 
parent diameter  as  mathematically  meas- 
ured varies  from  five  seconds,  when  he  is 
farthest  away,  to  thirteen  seconds,  when  he 
is  nearest. 

When  he  is  at  his  nearest  possible  distance 
from  us,  light  travels  from  Mercury  to  us 
in  a  little  more  than  four  minutes.  At  his 

102 


MERCURY 

greatest  possible  distance  we  could  not  re- 
ceive the  waves  of  light  that  he  sends  out 
in  less  than  twelve  minutes.  As  a  matter 
of  fact,  we  do  not  receive  them  at  all,  for, 
as  we  have  seen,  he  is  invisible  when  at  his 
greatest  possible  distance  from  us,  being 
then  on  the  far  side  of  the  sun. 

Another  cause  of  Mercury's  apparent 
change  in  brightness  is  due  to  the  fact  that, 
in  common  with  Venus,  he  goes  through 
phases  from  crescent  to  full  like  the  moon. 
This  is,  as  we  have  seen,  a  result  of  his  shin- 
ing only  by  reflected  light  and  of  his  orbit's 
being  between  ours  and  the  sun.  If  he  shone 
by  his  own  light,  he  would  be  at  his  nearest 
approach  to  us  a  very  brilliant  body  indeed. 
As  it  is,  his  dark  side  is  turned  toward  us 
when  he  is  nearest,  and  when  his  full  face  is 
illuminated  he  is  on  the  far  side  of  the  sun. 
We  see  half  of  his  face  when  he  is  at  greatest 
elongation;  but  he  is  brightest  when  we  see 
less  than  half,  because  he  is  then  nearer  to 
us,  and  the  difference  in  distance  more  than 
compensates  for  the  difference  in  illumina- 
tion. 

These  phases  cannot  be  seen  with  the  naked 
eye,  but  it  requires  only  a  small  telescope 
to  show  them,  and  a  very  charming  little 
103 


THE    WAYS    OF    THE    PLANETS 

moon-like  body  Mercury  is  when  we  see 
them.  His  horns  point  toward  the  east 
when  he  is  coming  toward  us  and  nearing 
inferior  conjunction,  and  when  he  is  back- 
ing away  from  us  and  going  toward  greatest 
western  elongation  they  point  toward  the 
west.  It  was  through  the  blunting  of  one 
of  these  horns  when  the  planet  was  in  cer- 
tain positions  that  a  mountainous  surface 
was  suspected,  so  great  is  the  significance 
of  small  details  in  observations. 

As  a  mere  place  from  which  to  view  the 
other  bright  bodies  Mercury  would  be  far 
superior  to  the  earth.  He  not  only  has  the 
sun  nearly  seven  times  larger  in  appearance 
at  its  mean  distance  than  we  see  it,  but,  being 
himself  nearest  the  sun,  all  the  other  planets 
are  outer  planets  in  relation  to  him,  and  all 
have  their  discs  fully  illuminated. 

The  earth  and  the  moon,  as  seen  from 
Mercury,  would  show  as  a  splendid  pair 
of  stars  circling  about  each  other,  the  earth 
more  brilliant  than  any  first-magnitude  star, 
and  the  moon  of  the  third  magnitude,  or 
about  as  bright  as  Phecda,  the  star  at  the 
bottom  of  the  bowl  of  the  Big  Dipper,  just 
under  the  beginning  of  the  handle.  The 
earth  would  show  a  disc  of  about  twenty 
104 


MERCURY 

seconds,  and  the  moon  one  of  about  eight 
seconds,  with  a  distance  between  them  of 
about  871  seconds.  Some  idea  of  what  this 
distance  is  may  be  had  if  one  knows 
Mizar,  the  star  at  the  bend  of  the  handle 
of  the  Dipper,  and  its  tiny  shining  atten- 
dant, Alcor.  These  two  stars  are  708  seconds 
apart.  The  distance  between  them  is  about 
equal  to  one-third  of  the  diameter  of  the 
moon  as  measured  from  the  earth.  It  does 
not  appear  to  be  nearly  so  much  as  that, 
and  some  persons  have  difficulty  in  separat- 
ing the  two  stars;  but  the  moon  is  not 
only  inconstant  but  deceptive,  and  owing  to 
its  brilliancy  seems  always  proportionately 
larger  than  it  really  measures. 

Venus  would  appear  from  Mercury  as 
much  as  four  times  as  large  as  she  seems  to 
us — a  veritable  little  moon,  and  always  full, 
her  size  varying  slightly  as  Mercury  speeded 
back  and  forth  from  the  farthest  to  the  near- 
est point  in  his  orbit,  changing  the  extreme 
of  the  distance  between  them  from  one 
hundred  and  ten  million  to  less  than  twenty- 
four  million  miles.  If  Mercury  needed  a 
moon,  he  could  well  find  some  consolation 
for  his  lack  of  it  in  the  presence  of  the  lovely 
Venus  in  his  sky. 

105 


THE    WAYS    OF    THE    PLANETS 

MERCURY'S  SIZE  AND  THE  CONSEQUENCES  OF  IT 

Mercury  is  the  smallest  of  all  the  major 
planets.  His  diameter  is  about  three  thou- 
sand miles.  It  is  only  about  nine  hundred 
miles  greater  than  that  of  our  moon.  The 
surface  of  Mercury  is  only  one-seventh  that 
of  the  earth,  and  his  volume  only  one- 
twentieth.  Jupiter  and  Saturn  each  have  a 
satellite  that  is  considerably  larger. 

Mercury  would  make  a  splendid  satellite 
or  a  giant  asteroid,  but  as  a  planet  seems 
hardly  to  have  had  a  fair  chance  in  life. 
For  being  a  small  planet  means  something 
more  than  being  constructed  on  smaller 
lines  than  some  others  are.  It  means  a  dif- 
ference in  physical  development.  It  means 
less  power  to  hold  the  gases  that  compose 
an  atmosphere,  which  is  the  cover  that  shields 
the  planets  from  the  too  burning  rays  of  the 
sun  and  keeps*  their  internal  heat  from  radi- 
ating too  quickly  into  space.  It  means  less 
power  to  resist  the  tidal  friction  that  the 
parent  body  uses  as  a  brake  to  retard  rota- 
tion. It  means  a  shorter  time  of  activity 
in  life,  and  a  long,  dull,  monotonous  old  age. 

The  nucleus  that  was  detached  from  the 
great  spiral,  or  the  portion  of  nebula  that  was 
106 


MERCURY 

separated  in  whatever  way  from  the  parent 
body,  to  form  Mercury  chanced  to  be  a 
small  one.  Being  small,  it  was  unable  to 
add  materially  to  its  mass  by  attracting 
other  particles  to  it  through  the  power  of 
gravitation,  as  a  larger  planet  might  do,  and 
thus  Mercury  was  doomed  to  develop  with 
the  limitations  that  nature's  law  has  decreed 
as  inevitable  in  the  small  bodies  of  our  solar 
system,  be  they  planets,  satellites,  or  aster- 
oids. Of  these  limitations  the  first  and  most 
far-reaching  in  its  effect  is  the  feebleness  of 
its  force  of  gravity,  or  power  to  attract  other 
bodies. 

Mercury's  force  of  gravity  is  small.  It 
is  smaller  than  that  of  any  of  the  other 
planets.  It  is  a  little  less  than  one-quarter 
that  of  the  earth.  The  same  weight  of 
feathers  that  would  compose  a  pillow  here 
would  make  a  whole  feather  bed  on  Mercury. 
Any  object  weighing  one  hundred  pounds 
here  would  weigh  only  twenty-four  there. 
The  materials  composing  our  earth  and  all 
the  planets  are  held  together  only  by  the 
force  of  gravity.  The  air  we  breathe  would 
dart  off  into  space  with  almost  incredible 
fleetness  if  the  earth  had  not  sufficient  gravi- 
tative  force  to  hold  it.  Its  particles  are 
107 


THE    WAYS    OF    THE    PLANETS 

struggling  all  the  time  to  get  beyond  this 
power.  The  lightest  of  them  do  get  beyond 
it  and  are  lost,  and  the  less  power  we  have 
to  hold  them  the  sooner  they  leave  us.  The 
greater  the  mass  of  a  body,  the  rarer  the 
gases  it  can  hold  in  its  atmosphere,  for  this 
mysterious  force  which  pulls  everything 
toward  the  center  of  a  planet  depends  upon 
its  mass,  or  the  quantity  of  material  in  it. 
The  planet  may  be  very  large  because  it  is 
very  much  expanded.  It  may  be  gaseous 
even,  and  its  mass  would  then  be  very  small 
in  proportion  to  that  of  a  solid  body  of  the 
same  size.  As  it  condenses,  the  particles 
draw  closer  and  closer  together,  the  density 
increases;  but  the  mass  is  the  same.  It  is 
only  the  size  that  diminishes. 

So  a  planet  with  a  small  mass  starts  out  in 
life  with  a  disadvantage.  It  not  only  has 
little  power  to  grow  by  drawing  in  particles 
from  its  environment,  but  also  has  little 
power  to  hold  such  as  by  their  nature  are 
volatile  and  swift  of  motion,  as  the  mole- 
cules of  gases  are.  The  mass  of  Mercury 
is  not  exactly  known.  The  only  way  we 
have  of  measuring  the  masses  of  the  planets 
is  by  their  influence  through  gravitation  on 
other  bodies  near  them.  When  a  planet  has 
108 


MERCURY 

satellites,  the  movements  of  the  satellites  tell 
the  story,  and  by  mathematical  calculation 
the  amount  of  material  in  the  planet  can  be 
determined.  But  Mercury  has  no  satellite, 
and  the  only  way  to  determine  his  mass  is 
by  observation  of  his  influence  on  Venus, 
and  on  an  occasional  comet  which  passes 
near  enough  to  be  disturbed  by  the  planet. 
The  particular  comet  which  has  been  useful 
in  determining  the  mass  of  Mercury  is 
Encke's.  On  passing  near  the  sun  it  comes 
sometimes  near  Mercury,  and  the  pull  it 
has  repeatedly  received  from  that  little 
planet  on  such  occasions  is  thought  to  be 
largely  responsible  for  the  comet's  having 
become  a  part  of  the  solar  system.  The 
changes  in  its  orbit  caused  by  these  en- 
counters show  the  power  of  Mercury,  and 
hence  the  mass. 

In  these  ways  the  mass  of  Mercury  has 
been  found,  with  reasonable  belief  in  its  ac- 
curacy, to  be  about  three  one-hundredths 
that  of  the  earth.  Yet  there  are,  indeed, 
considerable  differences  regarding  it  among 
astronomers.  The  exact  figures  are  not  im- 
portant to  any  but  the  close  student.  It  is 
certain  that  the  mass  of  Mercury  is  very 
small — so  small  that  the  planet  probably 
109 


THE    WAYS    OF    THE    PLANETS 

never  had  much  atmosphere,  and  almost 
undoubtedly  has  none  to  speak  of  now. 
The  planet  could  not  hold  any  molecule 
moving  faster  than  two  and  forty-five 
one  -  hundredths  miles  a  second,  and  few 
gases  move  as  slowly  as  this.  The  pro- 
portion of  light  that  Mercury  reflects  to 
that  which  he  receives  also  points  to  a  prob- 
able scarcity  of  atmosphere.  If  he  had  an 
atmosphere,  it  would  have  clouds.  Clouds 
have  a  very  high  reflecting  power,  giving 
out  about  seventy- two  per  cent,  of  the  light 
that  falls  upon  them.  Mercury  reflects  only 
fourteen  per  cent,  of  the  light  he  receives, 
which  shows  at  least  a  lack  of  clouds,  and 
something  more.  It  indicates  a  hard,  dark, 
almost  metallic  surface,  and  a  very  con- 
siderable density.  Density,  however,  is  the 
only  quality  in  the  possession  of  which  Mer- 
cury seems  to  occupy  a  middle  ground  among 
the  planets,  being  slightly  less  dense  than 
either  Venus,  or  Mars,  or  the  earth.  The 
earth  is  the  densest  of  all  the  planets,  and  it 
is  about  one-third  more  dense  than  Mer- 
cury. Density  is  simply  the  closeness  with 
which  the  particles  composing  a  body  are 
packed  together.  A  piece  of  gold,  for  example, 
is  denser  than  a  piece  of  iron  of  the  same  size, 
no 


MERCURY 


WHAT  THE   SUN   DOES    FOR   MERCURY 

It  is  probable  that  Mercury  has  no  alter- 
nations of  light  and  darkness,  causing  day 
and  night  such  as  we  know  them.  That  is, 
the  planet  does  not  rotate  on  its  axis  in  such 
a  way  as  to  turn  first  one  side  and  then 
the  other  toward  the  sun  as  the  earth  does. 
In  this,  as  in  some  other  things,  Mercury 
must  accept  the  fate  that  overtakes  many 
other  small  bodies  which  revolve  around 
large  ones — that  of  our  moon,  for  instance, 
and  the  satellites  of  some  of  the  other 
planets.  Working  under  the  law  of  gravita- 
tion, which  gives  such  power  to  the  large 
bodies,  the  sun  has  so  retarded  the  rotation 
of  Mercury  that  the  planet  now  makes  but 
one  rotation  on  its  axis  during  one  circuit 
around  that  central  body,  and  so  keeps 
always  the  same  face  toward  the  sun.  Some 
astronomers  do  not  regard  this  as  having 
been  wholly  proved;  but  all  the  later  ob- 
servations of  Mercury  strongly  indicate  that 
it  is  the  fact,  and  it  is  coming  to  be  more 
and  more  regarded  as  established. 

But,  even  if  this  is  the  predicament  into 
which  Mercury  has  come,  the  planet  is  prob- 
iii 


THE    WAYS    OF    THE    PLANETS 

ably  not  in  so  bad  a  plight  as  many  another 
body  to  which  the  same  sort  of  thing  has 
happened.  The  extreme  eccentricity  of  his 
orbit,  which  has  given  him  the  true  mer- 
curial temperament,  resulting  in  sprightli- 
ness,  agility,  and  changeableness,  is  account- 
able for  some  mitigating  circumstances.  The 
sun  may  hold  him  so  that  he  cannot  turn  his 
face  away  from  that  luminary;  but  it  cannot 
keep  him  from  rotating  on  his  axis  at  a  uni- 
form rate  of  speed,  and  from  this,  combined 
with  the  vagaries  caused  by  his  eccentric 
orbit,  come  some  interesting  things. 

Since  Mercury  is  less  than  two-thirds  as 
far  from  the  sun  at  perihelion  as  he  is  at 
aphelion,  there  is  a  corresponding  variation 
in  his  rate  of  speed.  When  he  is  nearest  the 
sun,  at  perihelion,  he  darts  along  at  the  rate 
of  thirty-five  miles  a  second ;  at  aphelion,  when 
he  is  farthest  from  the  sun,  he  travels  only 
twenty-three  miles  a  second.  Twenty-three 
miles  in  one  second  is  not  exactly  a  snail's 
pace,  terrestrially  considered,  and  it  is  faster 
than  the  earth  moves  at  any  time;  but  the 
planet  was  named  Mercury  because  of  his 
swiftness,  and  we  would  not  expect  much 
lagging  even  when  he  is  moving  at  his  slowest 
gait.  This  difference  in  speed  in  different 

112 


MERCURY 

parts  of  his  orbit  causes  what  is  called  the 
librations  of  Mercury.  When  he  is  travel- 
ing at  his  swiftest  pace  he  gets  a  little  ahead 
of  his  rotation,  the  speed  of  which  is  uni- 
form, and  thus  throws  the  sunlight  some- 
what farther  around  on  one  side.  When  his 
speed  decreases,  he  falls  behind  his  time  of 
rotation,  and  thus  gets  a  little  more  sunlight 
on  the  other  side.  Thus,  during  each  revo- 
lution he  juggles  the  sunlight  a  little  farther 
around  him  than  he  could  if  he  were  a  more 
steady-going  planet. 

These  librations  result  in  there  being  two 
strips  on  the  surface  of  Mercury — one  on 
each  side — which  undoubtedly  have  a  day 
and  night,  varying  in  length  in  the  different 
parts  of  the  strips.  The  part  that  lies  near- 
est the  illuminated  side  of  the  planet  has 
alternate  periods  of  sunlight  and  darkness, 
each  of  considerable  duration,  while  that 
part  nearest  the  dark  side  has  merely  a 
glimmer  of  sunlight  every  eighty-eight  days, 
which  is  Mercury's  sidereal  year,  or  the  time 
required  for  him  to  make  one  revolution 
around  the  sun.  These  two  strips  on  which 
the  light  varies  comprise  about  one-eighth 
of  the  surface  of  Mercury.  One  half  of  his 
entire  surface  is  always  light,  and  of  the  other 


THE    WAYS    OF    THE    PLANETS 

three-eighths  are  always  dark.  It  is  this 
dark,  cold  side  that  is  turned  toward  us 
when  Mercury  is  nearest  to  us. 

It  is  possible  that  on  those  parts  of  Mer- 
cury where  the  sunlight  and  darkness  are 
unstable  there  may  be  something  resembling 
a  tolerable  temperature.  They  are  some- 
thing more  than  a  thousand  miles  in  breadth, 
and  perhaps  near  the  center  of  them  the  sun 
may  give  heat  sufficient  to  enliven  and  yet 
not  burn.  More  than  likely,  they  are  alter- 
nately scorched  and  frozen.  For  it  takes 
more  than  the  mere  presence  of  sunlight  to 
make  a  climate  tolerable.  Atmosphere  is 
what  is  necessary,  and  we  have  seen  that 
Mercury  has  probably  lost  practically  all 
his  atmosphere  long,  long  ago.  An  atmos- 
phere absorbs  much  of  the  radiant  energy 
that  comes  from  the  sun  before  it  reaches 
the  more  solid  parts  of  a  planet,  and  it  also 
acts  as  a  blanket  in  preventing  the  too  rapid 
escape  of  such  heat  as  the  planet  may  have 
acquired.  Thus  it  has  the  doubly  beneficent 
office  of  tempering  the  rays  that  would  other- 
wise be  scorching  and  of  hindering  a  radia- 
tion that  would  leave  the  planet  stiffened 
and  frozen. 

Stiffened  and  frozen  is  what  the  dark  side 
114 


MERCURY 

of  Mercury  undoubtedly  is.  The  sun  has 
never  shone  upon  it  since  Mercury  became 
a  solid  body.  All  the  inherent  heat  it  had 
has  long  since  passed  off  into  space,  and  its 
temperature  must  be  somewhere  near  the 
absolute  zero.  The  absolute  zero  is  the 
point  in  temperature  where  all  known  sub- 
stances become  solid.  It  is  more  than  450° 
below  the  Fahrenheit  zero,  or  more  than 
350°  lower  than  any  temperature  recorded 
in  our  arctic  regions — a  degree  of  cold  un- 
thinkable to  any  but  the  scientist. 

On  the  other  side  of  Mercury  the  heat  is 
beyond  anything  we  have  any  notion  of. 
With  an  equal  atmosphere  it  would  receive 
from  the  sun  six  thousand  times  as  much 
light  and  heat  as  Neptune  on  an  equal  space, 
and,  on  an  average,  seven  times  as  much  as 
the  earth.  At  Mercury's  distance  from  the 
sun  his  hot  side  would  be  more  than  300° 
above  zero,  if  there  were  absolutely  no  at- 
mospheric protection.  Even  though  tem- 
pered by  a  thin  atmosphere,  as  it  may  be, 
the  heat  on  this  side  is  still  probably  enough 
to  boil  away  any  water  that  might  be  there 
and  to  change  some  other  substances  from 
what  we  regard  as  their  normal  state. 

Stability,  at  least,  is  a  quality  of  the  hot 
9  115 


THE    WAYS    OF    THE    PLANETS 

and  the  cold  side  of  Mercury.  Scorched  and 
seared  and  desolate  of  life,  as  we  know  it,  the 
one  side  lies  under  a  blazing,  dazzling  sun. 
Cold  and  hard  and  bleak,  and  no  less  desolate, 
the  other  side  turns  its  face  toward  the  dark- 
ness of  space.  Thus  they  will  remain  until 
the  end  of  time.  And  let  us  hope  that,  when 
the  final  catastrophe  occurs  and  a  new 
nebula  is  formed,  the  matter  composing 
Mercury  may  find  a  place  in  a  larger  mass, 
and  in  its  new  incarnation  have  a  fuller  and 
larger  life. 

It  is  the  atmosphere  also  which  causes  twi- 
light, as  well  as  the  gradual  changing  from 
heat  to  cold.  With  no  atmosphere,  we  would 
drop  from  full  daylight  to  the  darkness  of 
starlight  at  the  setting  of  the  sun.  So,  with 
the  thin  air  that  Mercury  probably  has  (if 
he  has  any),  the  two  zones  which  are  alter- 
nately light  and  dark,  and  hot  and  cold,  are 
not  much  better  off  than  the  parts  which  are 
permanently  either  light  or  dark.  They  are 
plunged  alternately  from  the  temperature 
and  light  of  the  hot  side  of  Mercury  to  the 
temperature  of  the  cold  side,  with  few  grada- 
tions to  prepare  them  for  such  extremes. 
Thus  the  only  part  of  the  planet  that  might 
be  expected  to  have  any  variations  of  sea- 
116 


MERCURY 

sons  fulfils  the  expectation  with  little  satis- 
faction. 

The  only  changes  in  climate  which  may 
have  an  appreciable  effect  are  mainly  those 
caused  by  the  eccentricity  of  Mercury's 
orbit,  which  carries  him  so  near  the  sun  at 
certain  times  and  so  comparatively  far  away 
at  others.  When  he  is  nearest  the  sun  he 
receives  more  than  twice  as  much  heat  and 
light  as  when  he  is  farthest  away.  At 
aphelion  he  receives  four  times  as  much 
heat  and  light  as  the  earth.  At  perihelion 
the  amount  of  heat  and  light  is  increased  to 
more  than  nine  times  that  of  the  earth. 
Since  it  takes  Mercury  a  little  more  than 
twelve  weeks  to  make  one  revolution  around 
the  sun,  he  passes  from  nearest  distance 
to  farthest,  or  the  reverse,  every  six  weeks. 
And  thus,  as  viewed  from  the  planet,  the 
sun  expands  gradually  for  six  weeks  until 
it  has  increased  its  diameter  two  and  one- 
half  times,  and  the  next  six  weeks  it  dimin- 
ishes in  the  same  proportion.  At  such  times, 
of  course,  the  amount  of  heat  is  more  or  less 
according  to  the  planet's  distance  from  the 
sun;  but  all  the  time  it  is  very  great. 

Moreover,  it  is  believed  that  the  axis  on 
which  Mercury  rotates  stands  perpendicular 
117 


THE    WAYS    OF    THE    PLANETS 

to  his  orbit.  This  being  the  case,  there  would 
be  on  Mercury  no  change  of  seasons  such  as 
the  earth  has.  The  earth's  axis  is  inclined 
a  little  more  than  twenty-three  degrees  to 
its  orbit,  and  from  this  we  get  the  sun's  rays 
in  a  great  variety  of  directions  and  different 
degrees  of  obliquity,  causing  the  seasons,  as 
we  know  them,  in  grateful  variation.  With 
the  axis  perpendicular,  as  it  probably  is  in 
the  case  of  Mercury,  the  sun's  rays  fall  on 
the  face  of  the  planet  always  with  the  same 
degree  of  directness,  the  only  relief  from 
their  greatest  heat  being  when  the  planet 
backs  away  from  the  sun  every  six  weeks, 
and  when  in  his  librations  he  turns  first  one 
sun-burned  cheek  and  then  the  other  tow- 
ard the  coolness  of  space. 

Thus  we  must  regard  the  smallest  of  our 
family  of  planets,  Mercury,  as  always  the 
dwarf  among  us,  with  never  a  fair  chance 
to  develop  a  rich  and  luscious  life  according 
to  our  ideas  of  such  a  life.  Beaten  by  the 
sun's  hard  rays,  and  with  no  sufficient  at- 
mospheric protection;  pulling  always  at  his 
tether,  but  held  firmly  with  his  face  to  the 
center;  circling  at  times  with  mercurial 
swiftness  and  thus  cheating  the  sun  into 
sending  its  rays  farther  toward  the  dark, 
118 


MERCURY 

cold  side  of  him  than  it  otherwise  would,  and 
with  all  his  defects  from  a  human  point  of 
view,  we  may  still  regard  him  as  a  right  mer- 
ry, roguish  little  planet,  after  all.  He  may  be 
prematurely  aged,  he  may  have  missed  many 
experiences  that  the  larger  planets  are  hav- 
ing, he  may  have  a  long  time  to  wait  for 
the  final  change  that  will  reunite  us  all; 
but  he  is  not  lying  in  sluggish  inactivity 
until  it  comes. 

In  view  of  the  fact  that  he  is  the  only 
planet  that  twinkles,  may  it  not  suggest, 
when  we  see  his  ruddy  face  peering  through 
the  thick  atmospheric  mists  near  our  hori- 
zon, that  the  impish  little  body  is  winking 
at  us,  and  that  it  may  be  with  planets  as  it 
is  with  people:  they  may  not  always  be  in 
an  unfortunate  plight  because  their  fate  is 
different  from  ours? 

TRANSITS 

Occasionally  Mercury  passes  at  inferior 
conjunction  between  us  and  the  disc  of  the 
sun,  appearing  like  a  black  spot  against  the 
sun,  and  thus  makes  what  we  call  a  transit. 
Because  the  planet  is  so  small,  his  transit 
across  the  sun  cannot  be  seen  with  the  naked 
119 


THE    WAYS    OF    THE    PLANETS 

eye;  but  it  is  an  interesting  phenomenon 
to  those  who  can  view  it  with  a  telescope, 
though,  apparently,  astronomers  do  not  re- 
gard it  as  having  any  great  scientific  im- 
portance. It  is  during  a  transit,  however, 
that  we  watch  for  confirmation  of  the  theories 
concerning  Mercury's  atmosphere,  which,  if 
it  were  a  reality,  would  show  a  diffused  light 
about  the  planet;  and  until  this  question  is 
settled  beyond  any  dispute  it  will  always 
come 'up  at  the  time  of  a  transit  of  Mercury. 
At  nearly  every  transit  some  observer  sees 
these  indications  of  an  atmosphere;  but  the 
better  the  telescope,  the  less  they  seem  to 
be  seen.  Hence  it  is  probable  that  there  is 
an  illusion  somewhere  either  of  eye,  or  instru- 
ment, or  mind,  and  that  the  majority  opin- 
ion, which  accords  to  Mercury  practically 
no  atmosphere,  is  about  the  correct  one. 

These  transits  occur  at  intervals  of  seven, 
thirteen,  or  forty-six  years,  according  to  the 
position  of  the  earth.  They  would  occur 
every  time  that  Mercury  passed  inferior  con- 
junction if  the  earth's  orbit  and  that  of 
Mercury  were  in  exactly  the  same  plane. 
But  the  orbit  of  Mercury,  we  have  seen,  is 
tilted  out  of  the  plane  of  the  ecliptic,  which 
marks  our  orbit,  seven  degrees,  so  that  the 
120 


MERCURY 

only  time  the  earth  and  the  planet  are  any- 
where nearly  in  the  same  plane  is  when  they 
are  at  or  near  the  points  where  their  orbits 
cross  each  other. 

The  earth  is  near  the  two  points  where 
Mercury  crosses  the  ecliptic  about  May  8th 
and  November  gth,  so  that  transits  can  oc- 
cur only  near  these  dates.  Mercury  passes 
these  points  four  times  every  year,  or  once 
in  each  revolution  around  the  sun.  But  the 
earth  is  not  always  there  at  the  same  time, 
and  it  is  because  of  this  that  transits  occur 
only  in  periods  of  seven,  thirteen,  or  forty- 
six  years.  They  occur  more  frequently  in 
November  than  in  May.  The  last  transit 
was  in  November,  1907.  The  next  will  be 
on  November  7,  1914,  and  there  will  not  be 
another  in  November  until  1927,  an  interval 
of  thirteen  years.  But  at  the  point  where 
the  May  transits  occur  there  will  be  one  on 
May  7,  1924. 


XI 

VENUS 

OF  all  the  planets  lovely  Venus  is  the  one 
that  is  best  known  and  most  admired. 
It  far  exceeds  all  the  other  planets  in  bril- 
liancy and  beauty  when  as  an  evening  star 
it  hangs  in  gracious  silvery  softness  above 
the  sun,  which  has  just  passed  below  the 
horizon;  and  it  is  not  less  surpassing  in 
loveliness  when  as, a  morning  star  it  conies 
into  view  shortly  before  the  sun  rises,  its 
glowing  face  still  silvery  and  bright,  but 
yet  tinged  with  the  rosy  flush  of  the  eastern 
morning  sky. 

In  either  position  it  never  twinkles  as 
Mercury  sometimes  does,  but  shines  so 
steadily  and  softly  that  at  times  its  disc 
can  almost  be  seen  with  the  naked  eye,  and 
it  has  such  brilliancy  that  its  light  can  often 
be  seen  in  the  daytime,  if  one  knows  when 
and  how  to  look  for  the  planet.  At  its 
brightest  it  frequently  throws  a  light  suffi- 

122 


VENUS 

ciently  strong  to  cast  a  shadow,  as  one  may 
easily  prove  by  holding  a  book  or  some  other 
opaque  object  between  Venus  and  a  white 
background,  such  as  the  wall  of  a  white 
house.  It  is  six  times  as  bright  as  the  bright- 
est of  all  the  fixed  stars,  Sirius,  the  beauti- 
ful dog-star,  which  we  see  in  winter  chasing 
across  the  southern  skies  after  Orion. 

Venus's  superior  brilliancy  is  due  in  part 
to  the  fact  that  it  comes  nearer  to  the  earth 
than  any  other  planet;  but  it  is  also  intrin- 
sically brighter  than  any  of  the  others. 
From  equal  areas  it  reflects  almost  four  times 
as  much  light  as  Mercury  and  three  times  as 
much  as  Mars. 

WHEN  AND  WHERE  TO  SEE  VENUS 

When  Venus  appears  in  the  sky  she  is  not 
often  mistaken  for  any  other  planet.  Among 
all  the  planets  she  is  the  most  readily  recog- 
nized and  the  easiest  to  find.  This  is  due 
largely  to  her  extreme  brilliancy  and  a  pe- 
culiar silvery  appearance  that  none  of  the 
other  planets  have;  but  also,  in  part,  to  her 
limited  range  in  the  sky,  and  her  favorable 
situation  for  observation.  Unlike  Mercury, 
she  is  far  enough  away  from  the  sun  to  be 
123 


THE    WAYS    OF    THE    PLANETS 

seen  above  the  horizon  for  as  much  as  three 
hours  after  sunset,  and  is  then  sufficiently 
high  in  the  heavens  to  be  seen  free  from 
the  vapors  of  the  atmosphere  at  the  horizon. 
Yet,  being  one  of  the  inferior  planets,  with 
her  orbit  smaller  and  nearer  the  sun  than 
that  of  the  earth,  she  can  never  get  so  far 
from  the  sun  as  to  be  at  any  uncomfortable 
height  for  viewing,  and  hence,  when  she  can 
be  seen  at  all,  is  always  an  obvious  bit  of 
brilliancy  and  a  joy  to  the  beholder.  She  is 
never  higher  in  the  sky  than  forty-five  de- 
grees, which  is  half-way  between  the  horizon 
and  the  zenith,  and  is  never  farther  away 
from  the  sun  than  forty-eight  degrees.  One 
frequently  sees  a  bright  planet  higher  up  in 
the  heavens  than  this;  but  it  is  never  Venus 
nor  Mercury. 

We  first  begin  to  notice  Venus  in  the  eve- 
ning sky  about  six  weeks  after  she  has  passed 
superior  conjunction.  She  is  then  very  near 
the  sun,  and  sets  a  little  less  than  half  an 
hour  after  sundown.  Evening  by  evening 
she  grows  gradually  brighter,  mounts  higher 
and  higher  in  the  sky  and,  consequently, 
sets  correspondingly  later,  until  in  a  little 
more  than  seven  months  after  superior  con- 
junction, and  about  six  months  after  we  have 
124 


VENUS 

begun  to  watch  her,  she  reaches  her  greatest 
elongation  east  from  the  sun.  At  that  time 
she  is  usually  somewhere  near  forty-five 
degrees  above  the  sun,  and  is  a  very  lovely 
and  conspicuous  object  in  the  evening  sky, 
setting  a  little  more  than  three  hours  after 
sundown. 

From  this  point  she  begins  to  travel  back 
toward  the  sun,  still  becoming  brighter  each 
evening,  because  she  is  really  coming  nearer 
to  us;  and  in  about  four  or  five  weeks  she 
attains  the  greatest  brilliancy  that  she  will 
have  as  an  evening  star  during  the  particular 
revolution  she  is  making.  About  twelve 
days  after  her  brightest  she  will  reach  the 
point  where  she  seems  to  be  stationary  for  a 
time.  This  is  when  she  is  about  to  overtake 
us  in  our  journey  around  the  sun.  After 
a  short  pause  she  will  move  on  gradually, 
her  course  among  the  stars  then  being  retro- 
grade or  westward;  but  what  we  most 
notice  is  that  she  is  drawing  nearer  to  the 
sun,  setting  earlier  each  evening,  and  be- 
coming more  and  more  difficult  to  see.  At 
the  end  of  about  three  weeks  she  is  in  in- 
ferior conjunction,  on  a  line  between  us  and 
the  sun,  and  invisible.  She  has  run  her 
course  as  an  evening  star  for  nine  and  a 
125 


THE    WAYS    OF    THE    PLANETS 

half  months,  and  has  been  visible  anywhere 
from  seven  to  eight  months,  the  time  of  her 
invisibility  depending  upon  the  eye  of  the 
observer  and  the  conditions  of  situation  and 
atmosphere. 

A  week  or  two  later  we  shall  find  her  a 
splendid  morning  star,  rising  nearly  an  hour 
earlier  than  the  sun.  About  three  weeks 
thereafter  she  will  be  at  her  brightest  as  a 
morning  star,  and  will  continue  to  be  very 
brilliant  for  some  weeks.  In  about  five  more 
weeks  she  will  have  reached  her  greatest 
elongation  west  of  the  sun,  and  will  rise 
about  three  hours  and  a  half  before  dawn. 
Then  she  will  begin  to  retrace  her  path, 
moving  eastward,  growing  smaller  all  the 
time  as  she  goes  farther  away  from  us,  and 
showing  a  slower  apparent  movement,  which 
gives  one  an  agreeable  sense  of  a  reluctant 
parting,  until  after  a  little  more  than  seven 
months  she  will  have  reached  the  sun  and 
will  again  be  in  superior  conjunction.  She 
has  then  been  a  morning  star  for  nine  and 
a  half  months,  and  has  been  visible  for  about 
the 'same  length  of  time  that  she  was  when 
she  shone  as  an  evening  star. 

This  is  a  brief  outline  of  a  typical  journey 
of  Venus  through  one  synodic  revolution. 
126 


VENUS 

She  began  one  of  these  journeys  on  July  5, 
1912,  being  then  in  superior  conjunction. 
During  the  autumn  of  this  year  and  the 
winter  of  1912-13  she  may  be  seen  shining 
with  great  brilliancy  in  the  west  at  sunset, 
and  a  few  hours  thereafter.  Early  in  Novem- 
ber, 1912,  she  and  Jupiter  will  both  be  in 
Scorpio,  where  they  will  approach  within 
two  degrees  of  each  other;  and  there  is  no 
doubt  that  their  presence  will  add  much 
charm  to  that  region  of  the  sky  during  the 
entire  autumn. 

About  the  middle  of  February,  1913, 
Venus  will  appear  half-way  up  to  the  zenith 
at  sunset.  She  will  then  be  at  her  greatest 
distance  east  of  the  sun,  and  will  be  very- 
bright;  but,  though  a  little  nearer  the  sun, 
she  will  be  still  brighter  shortly  after  the 
middle  of  March.  A  month  later  she  will 
be  invisible,  and  inferior  conjunction  will 
occur  on  April  24th.  During  most  of  May 
and  all  of  June  and  July  she  will  be  a  morn- 
ing star,  and  her  brilliant  beauty  will  well 
repay  an  early  morning  outlook.  She  will 
get  back  to  superior  conjunction  on  February 
u,  1914,  and  in  that  year  she  will  be  in  an 
ideal  situation  for  us  to  cultivate  a  more 
intimate  acquaintance  with  her.  From  the 
127 


THE    WAYS    OF    THE    PLANETS 

latter  part  of  March  to  November,  1914,  she 
will  be  the  brightest  star  in  the  western 
evening  sky,  and  will  do  much  to  enhance 
the  beauty  of  the  pleasant  summer  evenings 
of  that  year.  The  sturdy,  red-faced  Mars 
will  meet  her  on  August  5th,  a  little  more 
than  a  month  before  greatest  eastern  elonga- 
tion, and  might  almost  kiss  her  pale  cheek 
as  they  pass  within  one-sixth  of  a  degree 
of  each  other,  a  distance  equal  to  less  than 
one-third  of  the  diameter  of  the  moon. 

The  next  long  period  when  Venus  will  shine 
as  an  evening  star  will  comprise  the  spring 
and  early  summer  of  1916.  She  will  be  at  her 
greatest  distance  from  the  sun  during  the  last 
week  of  April,  and  will  not  pass  from  view 
until  about  the  first  of  July.  Then  again  she 
will  be  an  evening  star,  and  so  seen  in  the 
west  during  the  autumn  of  1917  and  the 
winter  of  1917-18,  reaching  greatest  eastern 
elongation  during  the  first  few  days  of  De- 
cember, 1917.  Her  next  return  to  the  eve- 
ning sky  will  be  for  the  first  eight  months  of 
1919,  and  the  next  will  be  for  the  winter  of 
1920-21  and  the  spring  of  1921. 

The  synodic  period  of  Venus  is  nearly  five 
hundred  and  eighty-four  days,  or  a  little 
more  than  one  year  and  seven  months, 

J28 


VENUS 

That  is,  the  planet  returns  to  the  same  posi- 
tion with  relation  to  the  sun  and  the  earth 
at  intervals  of  about  that  length.  The  in- 
tervals do  vary,  however,  as  much  as  a  week 
or  more,  owing  to  the  various  motions  and 
situations  of  the  planet  and  the  earth.  But 
every  eight  years  Venus  and  the  earth  come 
around  to  almost  exactly  the  same  relative 
position  with  each  other  and  the  sun  and 
the  stars,  and  thus  the  appearances  of  Ve- 
nus at  the  various  seasons  practically  repeat 
themselves  every  eight  years.  The  full 
splendor  that  she  is  to  offer  us  in  the  sum- 
mer of  1914  will  be  repeated  in  1922,  just 
as  that  of  1914  will  but  repeat  that  which 
she  showed  in  1906.  And  in  each  of  the 
intervening  years  she  will  have  again  the 
same  appearances  that  she  had  eight  years 
before. 

With  the  following  table  as  a  guide,  the 
appearances  of  Venus  can  be  followed  through 
a  number  of  years  with  sufficient  accuracy 
for  any  but  a  close  student  of  her  move- 
ments. The  exact  dates  of  elongations  and 
conjunctions  will  vary  a  few  days,  but  for 
at  least  two  or  three  multiples  of  eight  years 
not  enough  to  make  any  material  difference 
in  her  various  aspects. 
129 


THE    WAYS    OF    THE     PLANETS 

1913—192 1—1929—1937 

Greatest  eastern  elongation,  February  i2th.  In- 
ferior conjunction,  April  24th.  Greatest  western 
elongation,  July  3d. 


1914—1922—1930—1938 

Superior  conjunction,  February  nth.  Greatest 
eastern  elongation,  September  iyth.  Inferior  con- 
junction, November  27th. 


1915—1923—1931 

Greatest   western   elongation,    February   8th.    Su- 
perior conjunction,  September  i4th. 


1916 — 1924 — 1932 

Greatest  eastern  elongation,  April  26th.  Inferior 
conjunction,  July  5th.  Greatest  western  elongation, 
September  i4th. 

1917—1925—1933 

Superior  conjunction,  April  28th.  Greatest  east- 
ern elongation,  December  2d. 


1918 — 1926 — 1934 

Inferior  conjunction,  February  nth.  Greatest  east- 
ern elongation,  April  22d.  Superior  conjunction, 
November  25th. 

1919—1927—1935 

Greatest  eastern  elongation,  July  6th.  Inferior 
conjunction,  September  i4th.  Greatest  western  elon- 
gation, November  25th. 


1920 — 1928 
Superior  conjunction,  July  5th. 

130 


VENUS 

The  meetings  of  Venus  with  the  other 
planets  do  not,  however,  occur  with  this 
delightful  regularity.  They  all  are  moving 
about  in  their  own  ways,  and  engaged  in 
their  own  affairs,  and  only  the  earth  gets 
back  to  repeat  the  meeting  with  her  in  just 
eight  years.  These  eight-year  cycles  are 
due  to  the  fact  that  Venus  makes  thirteen 
revolutions  around  the  sun  while  the  earth 
makes  eight.  Her  journey  around  the  sun 
requires  a  little  less  than  two  hundred  and 
twenty-five  days  (224.70),  and  the  earth 
completes  its  revolution  in  a  little  more  than 
three  hundred  and  sixty-five  days  (365.25). 
So  at  the  end  of  about  two  thousand  nine 
hundred  and  twenty-two  days — which  equals 
eight  years — they  come  into  almost  exactly 
the  same  relative  positions  in  their  orbits 
with  which  they  started  out,  and  begin  the 
cycle  anew. 

DISTANCE    AND    BRILLIANCY 

The  mean  distance  of  Venus  from  the  sun 
is  67,269,000  miles.  Her  orbit  more  nearly 
approaches  the  form  of  a  circle  than  that  of 
any  other  planet.  It  is,  like  the  orbits  of 
the  other  planets,  an  ellipse,  but  of  such 

10  131 


THE    WAYS    OF    THE    PLANETS 

small  eccentricity  that  the  difference  be- 
tween her  greatest  and  least  distance  from 
the  sun  is  scarcely  more  than  a  million  miles. 
Light,  traveling  as  it  does,  at  the  rate  of  a 
little  more  than  one  hundred  and  eighty-six 
thousand  miles  a  second,  goes  from  the  sun 
to  Venus  in  about  six  minutes.  It  takes 
something  more  than  eight  minutes  for  light- 
rays  to  come  from  the  sun  to  us.  When 
Venus  is  nearest  the  earth,  her  silvery  beams 
come  swiftly  across  to  us  in  a  little  more 
than  two  minutes.  When  she  is  farthest 
from  us,  the  rays  of  light  require  a  few  sec- 
onds more  than  fourteen  minutes  to  travel 
over  the  distance.  She  is,  when  at  her 
greatest  distance,  more  than  one  hundred  and 
thirty-five  million  miles  farther  from  us  than 
when  at  her  nearest.  This  difference  is  due 
not  to  any  great  eccentricity  in  her  orbit,  or 
in  that  of  the  earth,  such  as  causes  Mer- 
cury's great  variations  of  distance,  but  to 
the  situation  of  the  two  bodies  in  their  orbits : 
they  are  nearest  together  when  they  are  on 
the  same  side  of  the  sun,  and  farthest  apart 
when  on  opposite  sides. 

Usually  at  inferior  conjunction  Venus  is  a 
little  more  than  twenty-five  million  miles 
from  the  earth.     At  her  nearest  possible  ap- 
132 


VENUS 

proach  to  us,  however,  which  takes  place  at 
inferior  conjunction,  when  the  earth  is  near- 
est the  sun  and  Venus  is  farthest  from  it,  a 
situation  which  occurs  only  once  or  twice  in 
a  century,  the  distance  between  us  and  the 
planet  is  only  a  little  more  than  twenty- 
three  million  miles.  This  is  nearer  than  any 
other  heavenly  body  ever  approaches  us, 
except  the  moon  and,  so  far  as  we  now 
know,  one  small  asteroid.  Also,  it  is  nearer 
than  Venus  comes  to  any  other  heavenly 
body  except  perhaps  Mercury.  Her  near- 
est approach  to  that  planet  is  also  about 
twenty- three  million  miles. 

Unfortunately,  our  comparative  proximity 
to  this  beautiful  planet  does  not  much  aid 
us  in  learning  anything  about  her  personal 
peculiarities.  Shining  only  by  reflected  light, 
and  being,  like  Mercury,  situated  nearer  to 
the  sun  than  the  earth  is,  when  she  comes 
around  to  the  same  side  of  the  sun  on  which 
we  are,  her  unillumined  side  is  turned  toward 
us,  and  at  the  point  of  very  closest  approach 
she  is  absolutely  invisible  to  the  naked  eye. 
Through  a  telescope,  however,  she  can  be 
seen  up  to  the  very  point  of  inferior  con- 
junction. What  we  see  then  is  a  mere  curved 
line  of  light,  so  thin  is  the  crescent  she  pre- 
133 


THE    WAYS    OF    THE    PLANETS 

sents;  but  it  is  always  apparent  except  when 
the  planet  makes  a  transit.  During  a  transit 
she  is  actually  in  our  line  of  sight  with  the 
bright  disc  of  the  sun,  and  is  neither  above 
nor  below  it,  as  at  the  ordinary  times  of 
inferior  conjunction.  The  slender  crescent 
that  we  ordinarily  see  offers  a  very  narrow 
field  for  observation. 

If  there  is  any  one  on  Venus  who  is  study- 
ing the  earth,  he  has  a  much  easier  task  than 
we  have  in  our  effort  to  learn  something 
about  her.  The  earth  is  not  only  somewhat 
larger  than  the  planet,  but  when  the  two 
bodies  are  nearest  together  the  disc  of  the 
earth  is  fully  illuminated,  and  so  must  show 
a  splendid  face;  and  then,  our  atmosphere 
probably  interferes  less  with  close  observa- 
tion than  that  of  Venus.  This  little  terres- 
trial system  would  undoubtedly  shine  as  a 
magnificent  pair  of  stars  if  observed  from 
Venus.  At  that  distance  our  moon  would 
appear  considerably  larger  than  Venus  ap- 
pears to  us  when  at  superior  conjunction, 
the  earth  would  seem  much  larger  than 
Venus  ever  does  to  us,  and  the  distance  be- 
tween them  would  seem  to  be  a  little  more 
than  the  apparent  diameter  of  the  full  moon 
as  we  see  it.  The  light  of  the  earth  must 


VENUS 

cause  much  more  of  a  shadow  than  we  ever 
get  from  the  light  of  Venus. 

It  has  been  suggested  that  light  from  the 
earth  is  responsible  for  a  dusky  illumination 
of  the  dark  side  of  Venus,  which  is  occasion- 
ally seen,  and  which  enables  us  to  distinguish 
her  entire  outline  even  when  only  the  merest 
line  of  a  crescent  is  really  illuminated.  It  is 
known  to  be  earth-shine  that  causes  what  is 
apparently  the  same  phenomenon  often  seen 
by  us  on  the  moon;  but  it  seems  that  there 
is  no  reason  to  think  that  our  earth,  at  its 
distance,  would  be  sufficiently  brilliant  to 
illuminate  Venus  even  so  slightly.  The 
cause  of  the  illumination  is  not  known;  but 
it  is  thought  that  it  may  have  some  elec- 
trical origin,  probably  similar  to  that  of  our 
aurora. 

Venus  has  the  same  phases  that  Mercury 
has.  She  shows  her  full  face  when  at  su- 
perior conjunction,  and  is  then  farthest  away 
and  smallest  to  our  view.  As  she  moves 
toward  us  she  first  becomes  gibbous,  and 
then,  at  eastern  elongation,  like  a  half -moon. 
As  she  comes  nearer  to  inferior  conjunction, 
and  hence  nearer  to  us,  she  becomes  a  thinner 
and  thinner  crescent,  and  as  she  goes  from 
inferior  to  superior  conjunction  these  phases 


THE    WAYS    OF    THE    PLANETS 

are  repeated  in  reverse  order.  We  see  less 
than  half  of  her  face  when  she  is  at  her 
greatest  brilliancy,  a  phase  which  usually 
occurs  when  she  is  about  forty  degrees  from 
the  sun,  as  she  is  a  few  weeks  before  and  af- 
ter inferior  conjunction.  A  very  small  glass 
will  show  the  phases  of  Venus.  They  have 
occasionally  been  seen  without  artificial  aid 
to  vision  by  an  exceptionally  good  eye. 
They  were  not  known,  however,  until  they 
were  discovered  by  Galileo  after  the  inven- 
tion of  the  telescope  in  1610. 

Venus  would  be  many  times  brignter  than 
she  ever  appears  if  the  entire  disc  of  the 
planet  could  be  seen  when  it  is  nearest  to 
us.  The  apparent  diameter  of  the  disc  at 
that  time  is  nearly  seven  times  larger  than 
when  we  see  it  at  the  planet's  greatest  dis- 
tance from  us.  When  Venus  is  in  superior 
conjunction  and  farthest  from  the  earth  the 
disc  measures  only  ten  seconds,  while  at 
inferior  conjunction  its  measure  is  nearly 
sixty-seven  seconds.  The  diameter  of  the 
moon  is  about  1,868  seconds,  so  one  could 
string  across  the  diameter  of  the  moon 
one  hundred  and  eighty-six  such  planets  as 
Venus  appears  to  be  when  at  her  smallest, 
and  only  twenty-seven  of  the  size  that  she 
136 


THE    LOVELY    CRESCENT    THAT    VENUS     SHOWS    WHEN     TO 
OUR    VIEW    SHE    IS    AT   HER    GREATEST    BRILLIANCY 

This   remarkable  photograph  was  made  at  the  Yerkes  Observatory 
by  E.  E.  Barnard. 


VENUS 

appears  to  be  when  at  her  largest.  Between 
these  two  extremes  of  size  she  changes  gradu- 
ally, day  by  day,  from  large  to  small  and 
small  to  large,  in  ceaseless  succession,  as  she 


•11 


RELATIVE      APPARENT      SIZE      OF      VENUS     AT     DIFFERENT 
PHASES   OF   ILLUMINATION 

She  shows  the  full  disc  when  farthest  away.  As  she  draws  nearer 
she  shows  first  the  half  moon  and  then  the  smaller  crescent.  She  is 
nearest  when  she  shows  the  larger  crescent.  She  is  brightest,  though, 
when  she  shows  the  smaller  crescent. 


approaches  the  earth  and  recedes  from  it  in 
her  orbital  journey.  Apparent  diameter  is 
determined  by  an  actual  measurement  of  the 
disc  of  a  planet,  and  in  the  case  of  Venus 
indicates  nothing  as  to  brightness.  When 
the  apparent  diameter  is  largest  she  is  not 
visible  to  the  naked  eye. 


THE    WAYS    OF    THE    PLANETS 
VENUS'S    LIKENESS   TO   THE   EARTH 

The  fact  that  of  all  the  planets  Venus  most 
resembles  this  good  little  earth  on  which 
our  present  lot  is  cast  gives  us  a  strong  feel- 
ing of  kinship  with  her,  and  a  more  lively 
interest  in  all  her  affairs  than  we  might  other- 
wise have.  She  and  the  earth  are  so  nearly 
of  one  size  that  they  are  often  referred  to 
as  twin  sisters.  There  is  a  difference  of  less 
than  three  hundred  miles  in  their  diameters, 
the  earth's  diameter  measuring  7,917  miles, 
and  that  of  Venus  7,629  miles.  The  sur- 
face of  the  planet  is  about  ninety-three  per 
cent,  as  extensive  as  that  of  the  earth;  its 
mass  is  a  little  more  than  eighty  per  cent., 
and  its  volume  about  ninety  per  cent,  as 
great  as  the  earth's.  Differing  so  little  in 
these  particulars,  it  follows  that  it  must  dif- 
fer very  little  in  density  and  gravity.  The 
earth  is  the  densest  of  all  the  planets,  and 
Venus  is  only  one-tenth  less  dense  than  the 
earth.  Its  force  of  gravity  is  not  quite  nine- 
tenths  that  of  the  earth.  A  removal  from 
the  earth  to  Venus  would  make  just  a  com- 
fortable reduction  in  one's  weight.  A  per- 
son weighing  one  hundred  and  seventy-five 
pounds  here  would  weigh  on  Venus  one  hun- 
138 


VENUS 

dred  and  fifty-four.  If  through  strength  of 
appetite  and  weakness  of  will  one  should 
take  on  two  hundred  pounds  of  too,  too  solid 
flesh  here,  transportation  to  Venus  would 
bring  about  an  instantaneous  reduction  to 
a  solid  one  hundred  and  seventy-six  pounds 
— as  much  of  a  reduction  as  would  be  com- 
patible with  health. 

Venus  must  have  begun  her  career  in 
much  the  same  way  that  the  earth  began 
its  career.  The  nebula  that  formed  her 
nucleus  was  probably  nearly  the  same  size 
(contained  about  the  same  amount  of  mat- 
ter) as  that  with  which  the  earth  began  its 
existence.  The  two  bodies  have  succeeded 
in  capturing  about  the  same  amount  of 
loose  material,  and  their  gravity  is  such  that 
they  can  hold  within  their  bounds  particles 
traveling  at  about  the  same  rate  of  speed. 
No  molecule  of  gas  coming  within  the  range 
of  Venus's  attraction  and  traveling  more 
slowly  than  six  and  thirty-seven  hundredths 
miles  per  second  can  escape  from  Venus, 
and  the  earth  can  hold  only  such  as  move, 
when  coming  within  its  own  attraction, 
with  a  less  speed  than  six  and  ninety-five 
one-hundredths  miles  per  second. 

The  earth  has  a  moon,  and  Venus  has  none; 


THE    WAYS    OF    THE    PLANETS 

but  that  may  be  because,  like  Mercury, 
Venus  is  too  near  the  sun  to  be  permitted 
to  retain  such  a  luxury.  It  is  likely  that 
if,  in  her  earlier  history,  she  had  within  the 
limit  of  her  gravitative  attraction  the  nucleus 
of  a  satellite,  it  would  have  been  taken  away 
from  her  by  the  stronger  attraction  of  the 
sun.  The  same  thing  would  have  happened 
to  us  if  we  had  been  a  little  nearer  the  sun. 
And  yet  in  1645  a  moon  belonging  to  Venus 
was  supposed  to  have  been  discovered,  and 
it  was  thought  to  have  been  seen  three  times 
within  the  rest  of  that  century,  and  four  times 
within  the  first  half  of  the  following  century. 
The  last  supposed  view  of  it  was  in  1791; 
it  has  never  been  seen  since.  There  is  little 
doubt  that  it  was  an  illusion  of  some  kind. 
Perhaps,  though,  Venus  has  not  the  same 
need  of  a  moon  that  we  have. 

ATMOSPHERE,  DAY  AND  NIGHT,  AND  SEASONS 

There  is  no  doubt  that  Venus  is  in  much 
better  plight  than  Mercury,  the  other  in- 
ferior planet,  in  regard  to  atmosphere.  Un- 
til recently  no  one  has  questioned  the  belief 
that  her  atmosphere  is  very  extensive — twice 
as  heavy,  perhaps,  as  that  of  the  earth, 
140 


VENUS 

dense,  and  full  of  clouds.  The  luminous 
ring  about  her,  shown  when  she  is  making 
a  transit  across  the  face  of  the  sun,  points 
to  a  heavy  atmosphere;  and  no  less  certain 
indications  of  it  are  given  in  the  faint  light 
which  stretches  beyond  the  termination  of 
the  horns  when  she  is  in  the  crescent  phase, 
near  inferior  conjunction.  Her  very  high 
reflecting  power  is  also  indicative  of  an 
atmosphere  laden  with  clouds.  White  clouds 
form  one  of  the  most  highly  reflecting  sur- 
faces known,  and  the  peculiar  brilliancy  of 
Venus  is  thought  to  be  in  great  part  due  to 
the  presence  of  large  masses  of  clouds  in  her 
atmosphere.  By  the  spectroscope,  and  in 
other  ways,  the  water  necessary  to  form 
clouds  is  shown  to  be  abundant  in  her  atmos- 
phere. Even  those  astronomers  who  doubt 
the  long-current  belief  in  the  large  extent 
of  her  atmosphere  concede  an  atmosphere 
of  more  or  less  density,  though  by  one  au- 
thority it  is  characterized  as  somewhat 
gauzy. 

There  is  one  vital  point  concerning  the 
development  of  Venus  upon  which  we  have 
as  yet  no  positive  knowledge:  the  length 
of  time  in  which  she  rotates  on  her  axis. 
This  is  unfortunate,  because  until  her  time 
141 


THE    WAYS    OF    THE    PLANETS 

of  rotation  is  known  we  cannot  know  much 
about  her  physical  condition.  Her  rotation, 
we  know,  determines  the  length  of  her  day 
and  night,  or  whether,  indeed,  she  has  any. 
The  time  of  it  has  been  calculated  to  be  any- 
where from  a  little  less  than  one  of  our  days 
to  two  hundred  and  twenty-five,  the  latter 
being  also  the  time  of  her  revolution  about 
the  sun.  Astronomers  of  equal  reputation 
have  come  to  exactly  opposite  results  in  their 
investigations.  To  one,  the  spectroscope  has 
indicated  the  short  day  and  night;  to  another 
it  has  shown  no  day  and  night,  but  a  planet 
with  one  face  forever  toward  the  sun,  like 
Mercury.  What  appeared  to  be  stable,  sur- 
face markings  have  been  observed,  but  have 
indicated  under  the  eyes  of  different  ob- 
servers both  the  short  day  and  no  day  at  all. 
The  disc  has  been  measured  during  a  transit, 
and  shows  so  little  flattening  as  to  indicate 
a  slow  rotation  and  the  long  day.  On  the 
other  hand,  the  best  authorities  think  it 
unlikely  that  at  the  distance  of  Venus  the 
sun  could  so  retard  the  planet's  rotation  as 
to  make  it  coincide  with  its  time  of  revolu- 
tion. Thus  the  question  is  still  an  open  one. 
The  truth  may  be  that,  owing  to  the  den- 
sity of  her  atmosphere,  the  surface  of  Venus 
142 


VENUS 

has  never  been  seen  at  all,  and  that  the  ap- 
parently stable  markings  are  but  clouds 
more  or  less  lacking  in  stability.  The  diffi- 
culty of  observing  Venus  will  probably  make 
it  impossible  to  determine  this  point  by 
visual  observation.  It  may  some  day  be 
settled  beyond  a  doubt  by  the  spectro- 
scope. In  some  way  it  will  surely  be  settled. 
Astronomers  have  too  often  made  possible 
what  seemed  to  be  impossible  for  us  to  doubt 
that  some  one  will  find  a  way  to  discover  this 
secret  of  Venus.  With  them  a  failure  to  prove 
a  conclusion  does  not  mean  to  abandon  the 
subject,  but  to  try  some  other  means  of  get- 
ting at  the  truth. 

The  sun  viewed  from  Venus  would  appear 
considerably  larger  than  it  does  to  us.  Its 
apparent  diameter  to  us  is  a  little  more 
than  thirty-two  minutes,  while  on  Venus  it 
would  be  something  more  than  thirty-eight 
minutes;  that  is,  it  would  appear  about 
one-fifth  larger  on  Venus  than  it  does  to  us. 
This  is  enough  to  make  a  material  difference 
between  the  two  planets  in  the  amount  of 
heat  and  light  they  receive.  Venus  receives 
nearly  twice  (1.9)  as  much  heat  and  light 
from  the  sun  as  we  receive,  but  less  than  one- 


THE    WAYS    OF    THE    PLANETS 

third  as  much  as  Mercury.  If  she  had  no 
atmospheric  protection,  there  is  no  question 
but  that  she  would  have  a  climate  disastrous- 
ly warm  for  a  race  of  beings  constituted  as 
we  are.  The  normal  temperature  of  an  un- 
protected body  at  the  distance  of  Venus  is 
about  158°  Fahrenheit  (70°  Centigrade). 

If  Venus  is  finally  proved  to  have  no  alter- 
nations of  day  and  night,  she  is  still  better 
off  than  Mercury,  who  has  practically  no 
atmosphere  to  protect  him  from  the  intense 
heat  of  the  sun.  How  much  protection  she 
has  depends  altogether  on  the  extent  of  her 
atmosphere.  It  is  probably  not  enough  to 
make  the  hot  side  comfortable  from  our 
point  of  view  ;  and  Venus,  being  undoubt- 
edly a  solid  body  with  no  internal  heat,  the 
cold  side  must  be  cold  beyond  anything  we 
have  any  conception  of.  But  there  may  be 
a  very  considerable  part  on  each  side  that, 
owing  to  the  refraction  of  light  by  the  atmos- 
phere, is  more  or  less  well  lighted,  and  is 
also  more  or  less  protected  by  this  same 
beneficent  atmosphere  from  deadly  ex- 
tremes of  heat  and  cold.  In  this  situation 
there  would  undoubtedly  be  lively  currents 
of  air  from  the  heated  side  to  the  cooler; 
but  even  these  may  in  some  way  carry  with 
144 


VENUS 

them  some  tempering  effects  on  the  climate, 
as  we  know  such  currents  do  here  on  the 
earth. 

If  it  should  prove  that  the  length  of  the 
day  and  night  on  Venus  is  something  near 
that  of  the  earth's  (and  this  seems  not  un- 
likely), she  would  then  be  indeed  more  like 
a  twin  sister  to  us.  Being  next  to  each  other 
in  our  distances  from  the  sun,  and  of  nearly 
the  same  size,  differing  but  little  in  density, 
mass,  volume,  and  force  of  gravity,  with  her 
greater  normal  heat  probably  reduced  by 
her  heavier  atmosphere  to  a  temperature 
producing  climatic  conditions  not  very  un- 
like ours,  and  with  not  very  different  alter- 
nations of  day  and  night,  we  might  well  be 
considered  more  nearly  related  than  any  of 
the  other  members  of  the  solar  family. 

The  seasons,  however,  on  Venus  and  the 
earth  would  not  have  much  resemblance  to 
each  other.  The  axis  of  the  earth  is  inclined 
to  the  ecliptic  nearly  twenty-three  and  one- 
half  degrees,  so  that  we  receive  the  sun's  rays 
with  varying  degrees  of  obliquity  during  our 
yearly  journeying  around  it,  which  is  the 
cause  of  our  agreeable  change  of  seasons. 
Venus  travels  with  her  axis  so  slightly  in- 
clined to  her  orbit  (a  little  more  than  three 
US 


THE    WAYS    OF    THE    PLANETS 

degrees)  that  each  particular  parallel  of  lat- 
itude receives  practically  the  same  amount 
of  sunlight  every  day  in  the  year,  though  at 
different  parallels  the  sun's  rays  strike  with 
varying  degrees  of  obliquity.  However  de- 
lightful or  disagreeable  the  climate  may  be, 
there  are  no  changes  of  seasons  to  speak  of, 
and  one  could  find  variety  only  by  going 
from  place  to  place  on  the  planet.  She  re- 
ceives no  compensation  for  this  monotony 
by  alternately  receding  from  and  approach- 
ing the  sun  as  Mercury  does,  or  by  librations, 
such  as  he  has.  Her  orbit  being,  as  we  have 
seen,  so  nearly  circular  as  to  permit  of  only 
small  variations  in  her  distance  from  the 
sun,  and  her  axis  so  nearly  perpendicular  to 
her  orbit,  it  follows  that  she  has  nothing  to 
mark  the  year;  and,  whether  she  turns  on  her 
axis  many  times  or  only  once  during  a  revo- 
lution, life  on  Venus  would  be  very  monoto- 
nous to  any  one  accustomed  to  our  delight- 
ful variety  of  climate  and  seasons.  Still, 
there  is  nothing  in  this  monotony  to  prevent 
Venus  from  being  a  fairly  comfortable  habita- 
tion in  some  parts  for  such  beings  as  inhabit 
the  earth.  The  only  real  obstacle  to  habit- 
ability  on  Venus  would  be  her  lack  of  rota- 
tion and  all  that  it  involves. 
146 


VENUS 

Since  we  are  not  sure  that  we  can  see  the 
surface  of  Venus,  we  cannot  say  what  that 
surface  is.  Nevertheless,  there  is  some  rea- 
son to  suspect  that  we  would  find  there 
mountains  of  vast  height.  Certain  irregu- 
larities have  been  observed  at  times,  of  a 
kind  to  indicate  mountains  covered  with 
snow,  extending  beyond  the  clouds.  They 
have  been  estimated  to  be  many  miles  higher 
than  any  mountains  we  have  on  earth,  their 
height  depending  somewhat  upon  the  tem- 
perament of  the  observer.  But  inasmuch 
as  these  same  high  mountains  have  some- 
times been  thought  to  be  only  masses  of 
clouds,  it  seems  hardly  safe  to  pronounce 
definitely  upon  them. 

TRANSITS 

On  rare  occasions,  when  Venus  is  in  infe- 
rior conjunction,  she  makes  a  transit,  and  can 
then  be  seen  as  a  black  dot  moving  over  the 
bright  face  of  the  sun.  Transits  can  occur 
only  when  the  earth  and  the  planet  are  near 
the  point  where  their  orbits  cross  each  other. 
The  earth  is  at  this  point  every  year  on 
June  7th  and  December  7th;  but  the  orbit 
of  Venus  is  such  that  she  is  there  on  the 

11  147 


THE   WAYS    OF    THE    PLANETS 

proper  dates  only  four  times  in  a  period  of 
two  hundred  and  forty- three  years.  In 
every  two  hundred  and  forty-three  years 
four  transits  take  place.  They  occur  in 
pairs,  eight  years  apart,  and  in  the  same 
month.  If  a  pair  occur  in  June,  it  will  be 
one  hundred  and  five  and  one-half  years 
after  the  last  one  of  the  pair  until  we  have 
the  first  of  the  December  pair  of  transits. 
After  that  it  will  be  one  hundred  and  twenty- 
one  and  a  half  years  until  we  have  the  first 
of  another  pair  of  June  transits. 

The  first  transit  of  Venus  that  was  scien- 
tifically observed  was  in  December,  1639. 
It  was  the  last  of  a  December  pair,  there 
having  been  a  transit  eight  years  before,  in 
December,  1631.  One  hundred  and  twenty- 
one  and  a  half  years  later,  in  1761,  a  June 
transit  occurred,  and  in  1769  another  one 
took  place  in  June.  Then  there  were  no 
more  for  one  hundred  and  five  and  one- 
half  years,  when  we  had  a  December  pair 
in  1874  and  1882.  The  next  ones  will  be  in 
June,  2004  and  2012. 

Great  importance  was  attached  to  those 

transits   that  occurred  in   1874  and   1882, 

because  they  were  expected  to  be  useful  in 

determining  with  greater  exactness  the  dis- 

148 


VENUS 

tance  of  the  sun.  Extensive  preparations 
were  made  for  scientific  observation  of  them; 
but  the  results  were  not  satisfactory,  largely 
because  the  atmosphere  of  Venus  prevented 
her  from  showing  a  sharp  outline  at  the 
moment  of  entering  upon  and  of  leaving  the 
face  of  the  sun.  The  main  scientific  value 
of  a  transit  of  Venus  now  is  in  the  oppor- 
tunity it  may  offer  to  investigate  the  nature 
of  her  atmosphere.  Even  though  that  in- 
teresting question  may  have  been  practically 
settled  before  another  transit  takes  place, 
it  will  be  important  to  know  to  what  degree 
the  phenomena  observed  at  the  next  transit 
confirm  the  decision. 

On  account  of  the  surpassing  brilliancy  of 
Venus,  the  brightest  of  all  the  heavenly 
bodies  after  the  sun  and  moon,  she  was  to 
the  ancients  the  most  important  of  all  the 
stars  and  planets.  She  was  the  supreme 
evening  and  morning  star.  As  evening  star 
she  was  known  as  Hesperus,  or  Vesper;  as 
a  morning  star  she  was  called  Phosphorus,  or 
Lucifer,  and  under  all  these  names  she  is 
frequently  mentioned  in  Greek  and  Latin 
and  kindred  literatures. 

The  symbol  of  Venus  is  ? ,  a  figure  which 
149 


THE    WAYS    OF    THE    PLANETS 

is  nothing  more  than  the  conventionalized 
form  of  a  looking-glass,  an  article  that  is 
often  pictured  in  the  hands  of  the  goddess 
for  whom  our  beautiful  planet  was  named. 
In  her  general  aspect  she  is  as  placidly  splen- 
did and  charming  as  ever  a  goddess  could 
be,  and  it  is  not  strange  that  the  happy  ears 
that  could  hear  such  strains  should  find  her, 
as  they  did,  singing  a  rich  contralto  in  the 
music  of  the  spheres.  Jupiter  and  Saturn, 
under  this  mythological  apportionment,  sang 
bass,  Mars  took  care  of  the  tenor  strains, 
and  the  high  soprano  was  carried  by  our 
little  dwarf  Mercury. 


XII 

MARS 

'T'HE  planet  that  varies  most  in  the  beauty 
1  of  its  aspect  is  Mars.  It  is  as  much  as 
fifty  times  brighter  when  it  is  nearest  to  us 
than  it  is  at  its  greatest  distance  from  us. 
At  its  brightest  it  is  many  times  more  bril- 
liant than  any  of  the  first-magnitude  stars; 
but  when  it  leaves  our  neighborhood  and 
goes  far  off  into  space  in  its  journey  around 
the  sun,  its  glory  is  so  dimmed  that  it  be- 
comes not  brighter  than  an  ordinary  second- 
magnitude  star,  such  as  the  pole-star,  and 
less  brilliant  than  the  brightest  stars  in  the 
Big  Dipper. 

These  extreme  changes  of  brightness  are 
due  not  so  much  to  any  great  distance  that 
Mars  goes  from  us  in  comparison  with  other 
planets  as  to  its  coming  so  very  near  to  us 
at  times.  It  is,  after  all,  a  small  body,  and 
no  great  distance,  as  heavenly  distances  go, 
is  required  to  make  it  show  so.  But  the 


THE    WAYS    OF    THE    PLANETS 

eccentricity  of  its  orbit  brings  it  sometimes 
very  near  us,  and  its  near  approaches  are 
at  a  time  when  we  can  see  its  entire  disc,  and 
not  a  mere  crescent,  such  as  we  see  when 
Venus  is  nearest  to  us.  Mars  does  not  come 
quite  so  near  to  us  as  Venus  comes,  but 
when  he  is  in  the  best  position  to  be  seen 
he  is  much  nearer  than  she  is  when  in  her 
best  position.  For  we  have  seen  that  Venus 
is  brightest  before  she  reaches  her  nearest 
position  to  us,  while  Mars  is  brightest  when 
he  is  at  his  nearest  to  us.  When  Venus  is  at 
greatest  elongation  she  is  three  times  farther 
away  than  Mars  is  at  his  nearest. 

HOW   TO   IDENTIFY   MARS 

But  with  all  his  variations  in  brilliancy 
and  beauty  Mars  remains  ever  a  charming, 
rosy-hued  planet,  shining  always  with  a 
steady,  clear  light,  and  when  once  we  have 
come  to  know  him  is  not  easily  mistaken 
for  any  other  planet,  or  for  any  of  the  brilliant 
stars  that  may  more  or  less  resemble  him  in 
color.  Red  in  varying  degrees  of  intensity 
is,  perhaps,  the  most  obviously  distinguish- 
ing mark  of  Mars;  but  his  own  character- 
istics are  never  more  distinct  than  when  his 
152 


MARS 

path  takes  him  into  the  region  of  the  two 
best-known  red  stars  in  the  heavens.  These 
are  Antares,  the  glowing  star  in  the  con- 
stellation Scorpio,  which  we  see  in  the  south- 
ern sky  during  the  summer,  and  ruddy 
Aldebaran,  which  shines  in  the  head  of 
Taurus  and  under  the  Pleiades  through  the 
bright  wintry  nights.  On  every  journey 
around  the  skies  Mars  passes  near  these  two 
stars.  They  are  both  in  the  constellations 
of  the  zodiac,  and  are  often  quite  near  to 
Mars,  as  well  as  to  the  other  planets  and  the 
moon.  The  stars,  though  of  the  same  color 
as  Mars,  are  much  more  jewel-like  than  the 
planet.  Mars  is  less  sparkling.  When  it  is 
small,  it  shows  a  placid,  rosy  little  disc,  with- 
out much  gaiety,  and  not  in  any  way  sug- 
gesting anything  martial;  but  at  its  largest, 
it  has  a  distinctly  flame-like  aspect,  which 
easily  suggests  why  it  was  named  for  the 
god  of  war. 

Mercury  is  the  only  planet  that  in  color 
even  suggests  Mars,  and  for  Mercury  it 
can  never  be  mistaken  after  one  has  once 
seen  the  two  planets.  Mercury,  we  know, 
is  always  very  near  the  sun;  but  when  visible 
at  all  is,  even  in  that  unfavorable  situation, 
always  as  bright  as  a  first-magnitude  star. 


THE    WAYS    OF    THE    PLANETS 

Mars  is  near  the  sun,  to  our  view,  only  when 
it  is  approaching  conjunction,  and  it  is  then 
so  far  from  us  that  it  always  appears  as  a 
rather  small  star,  and,  while  never  insig- 
nificant, is,  in  this  situation,  quite  incon- 
spicuous even  as  compared  with  the  rarely 
visible  Mercury. 

On  seeing  a  planet,  then,  sufficiently  high 
above  the  horizon  to  attract  one's  attention, 
one  may  be  sure  that  it  is  Mars  if  it  is  red, 
and  equally  sure  that  it  is  not  Mars  if  it 
does  not  show  this  color.  Under  certain 
atmospheric  conditions  the  sun,  moon,  and 
all  the  planets  sometimes  appear  red  when 
they  are  very  near  the  horizon;  but  in  this 
situation  there  is  always  something  other 
than  color  that  marks  them. 

If  its  color  is  not  a  sufficient  mark  by  which 
to  identify  Mars,  a  still  further  difference 
between  it  and  the  stars  is  its  markedly 
rapid  movement.  A  single  night  will  make 
a  sufficient  change  in  its  position  to  show  the 
planet  as  a  wanderer.  On  an  average,  it 
travels  over  about  four-tenths  of  a  degree 
in  the  heavens  in  one  day.  This  equals  more 
than  half  the  diameter  of  the  moon,  a  change 
of  position  sufficiently  great  to  be  easily 
detected. 


MARS 

WHEN  AND  WHERE   MARS   MAY   BE   SEEN 

Unlike  Mercury  and  Venus,  which  are 
never  far  from  the  sun,  and  can  be  seen  only 
for  a  comparatively  short  time  either  early 
in  the  morning  or  in  the  evening,  and  are 
never  very  high  up  in  the  skies,  Mars  may 
be  situated  so  that  it  can  be  seen  at  any  time 
of  the  night,  and  also  at  any  distance  from 
the  sun.  When  it  is  in  opposition  it  rises 
just  as  the  sun  sets,  and  is  then  in  view 
all  night.  At  this  time  it  is  nearer,  larger, 
and  brighter  than  at  any  other  time  in  the 
particular  revolution  it  is  then  making,  and, 
consequently,  is  in  the  best  position  to  be 
viewed  by  us  that  it  will  have  during  that 
revolution. 

Oppositions  differ,  however,  in  different 
revolutions,  and  some  show  us  the  planet 
more  splendidly  brilliant  than  it  appears  at 
others.  The  oppositions  at  which  Mars 
shows  most  brilliant  take  place,  fortunately, 
in  the  summer  and  early  autumn — the  sea- 
sons which  are  most  agreeable  for  outdoor 
observation.  He  is  then  traveling  through 
that  region  of  the  sky,  sparse  in  stars,  that 
lies  between  Sagittarius  and  Aries ;  and,  since 
the  ecliptic  there  runs  rather  low  in  the  sky, 


THE    WAYS    OF    THE    PLANETS 

he  can  easily  be  observed  at  any  time  in  the 
night  without  any  neck-breaking  postures. 

These  favorable  oppositions  occur  in  the 
summer  because  the  earth  is  in  line  in  the 
latter  part  of  August  with  that  point  in  the 
orbit  of  Mars  where  the  planet  makes  its 
nearest  approach  to  the  sun.  Oppositions 
never  occur  when  Mars  is  exactly  at  that 
point;  but  they  do  occur  when  he  is  very 
near  it,  and  at  such  times  we  see  him  in  his 
greatest  glory.  This  happens  once  every 
fifteen  or  seventeen  years.  But  at  any  sum- 
mer or  early -autumn  opposition  Mars  is 
not  very  far  from  this  nearest  point  to  the 
sun,  so  that  at  any  oppositions  during  these 
seasons  he  is  very  brilliant  and  almost  as 
bright  as  when  he  is  at  his  best. 

The  earth  is  in  line  in  the  winter  with  that 
part  of  Mars's  orbit  which  carries  him  far- 
thest from  the  sun,  and  at  opposition  then 
he  is  much  less  bright  than  at  the  summer 
oppositions.  He  is  at  the  same  time  in 
those  constellations  which  pass  nearly  over- 
head in  the  sky,  and  cannot  be  quite  so  com- 
fortably seen  at  all  times  in  the  night  as  he 
can  be  in  the  summer.  The  very  best  and 
most  brilliant  oppositions  occur  in  the 
latter  part  of  August  or  in  the  early  part  of 


MARS 

September;  the  least  favorable  ones  occur 
in  February.  The  others  vary  in  brilliancy 
according  to  their  distance  from  these  favor- 
able and  unfavorable  dates,  all  the  summer 
ones  being  quite  brilliant,  and  all  the  win- 
ter ones  much  less  so.  At  any  opposition, 
though,  however  unfavorable,  the  planet  is 
much  nearer  to  us  and  much  brighter  than 
when  in  conjunction. 

It  is  worth  one's  while,  even  at  some  in- 
convenience, to  see  Mars  at  whatever  time 
he  is  in  opposition,  for  he  is  a  delight  to  the 
observer,  and  always  notable  in  the  part  of 
the  skies  through  which  he  is  then  passing. 
There  are  some  aspects  of  the  planet  that 
are  so  charming  at  a  winter  opposition  that 
it  is  a  positive  loss  not  to  have  seen  him  at 
such  times.  He  is  more  isolated  and  con- 
spicuous in  the  summer;  but  he  fits  well  in 
that  gay  company  of  winter  stars  that  shine 
more  brilliantly  than  any  others,  and  we 
can  easily  feel  something  akin  to  family 
pride  as  we  watch  him  moving  so  graciously 
among  them. 

Mars  makes  a  complete  circuit  of  the  skies, 
and  comes  back  into  the  same  position  with 
relation  to  the  sun  and  the  earth  on  an 
average  every  seven  hundred  and  eighty  days, 


THE    WAYS    OF    THE    PLANETS 

which  makes  his  synodic  period  longer  than 
that  of  any  other  planet.  Owing  to  the 
great  eccentricity  of  his  orbit,  and  his  con- 
sequent unequal  motion  in  the  various  parts 
of  it,  the  synodic  period  varies  as  much  as 
thirty-five  or  thirty-six  days.  One  cannot 
say,  therefore,  without  computation  of  some 
length,  just  exactly  how  many  days  will 
elapse  between  any  two  single  oppositions. 
For  mere  purposes  of  naked-eye  observa- 
tion the  variations  in  the  synodic  period  of 
Mars  do  not  make  any  difference,  for  the 
planet  is  in  view  practically  all  night  for 
many  nights  before  and  after  opposition, 
with  changes  of  brightness  too  small  to  be 
noticed  by  an  untrained  eye.  For  at  least 
two  months  at  the  time  of  opposition  it  has 
almost  the  same  aspect  to  us.  At  that  time 
it  is  always  in  the  east  early  in  the  eve- 
ning, and  shines  all  night.  For  nearly  nine 
months  afterward  it  is  visible  and  con- 
spicuous in  the  evening  sky,  appearing  each 
evening  nearer  and  nearer  to  the  western 
horizon,  until  finally,  in  a  little  more  than  a 
year  after  opposition,  it  passes  behind  the 
sun  and  becomes  a  morning  star.  But,  as  it 
then  rises  before  the  sun  and  passes  across 
the  heavens  in  the  daytime,  it  is  invisible 
158 


MARS 

to  us.  It  is  pleasant,  however,  at  such  times 
to  know  that  as  the  sun  passes  across  the 
skies  in  its  daily  journey  Mars  is  up  there, 
within  a  certain  distance  from  it,  making  the 
same  journey  with  it,  beaming  down  upon 
us  with  the  same  lively  light  that  it  shows 
at  night,  and  could  be  as  well  seen  at  any 
time  but  for  the  too  dazzling  rays  of  the 
sun. 

Mars  will  be  in  conjunction  in  November 
of  this  year  (1912),  and  will  not  be  visible 
in  the  evening  during  1913  until  toward  the 
end  of  the  year.  The  next  opposition  after 
the  publication  of  this  book  will  occur  in 
January,  1914.  From  that  time  until  the 
following  autumn  the  planet  may  be  seen 
in  the  evening.  In  1915  Mars  will  not  be 
visible  in  the  evening  sky  until  late  in  the 
year.  After  November  it  will  be  in  the  east 
in  the  evening,  rising  earlier  each  evening, 
until  at  opposition,  early  in  1916,  it  will  rise 
at  sunset  and  will  be  visible  in  the  evening 
during  the  entire  summer  and  autumn  of 
that  year,  but  will  not  be  extraordinarily 
bright.  In  1917  it  will  be  again  invisible 
in  the  evening.  In  1918  it  will  be  in  opposi- 
tion in  the  early  spring,  and  will  shine  in 
the  evening  all  the  rest  of  that  year.  It 
159 


THE    WAYS    OF    THE    PLANETS 

will  not  be  visible  in  the  evening  in  1919, 
but  will  be  in  opposition  again  in  the  latter 
part  of  April,  1920,  and  will  shine  in  the 
evening  all  of  that  year  and  the  early  part 
of  the  next,  when  it  will  again  disappear 
from  evening  view  and  will  not  emerge 
again  until  it  is  nearing  a  fine  opposition 
that  will  take  place  just  at  the  beginning  of 
the  summer  of  1922.  The  planet  will  then 
be  in  the  constellation  Scorpio,  not  far  from 
Antares,  and  this  will  afford  an  excellent 
opportunity  to  see  these  two  ruddy  bodies 
near  together. 

In  1924  there  will  be  an  exceptionally 
brilliant  opposition,  which  will  occur  during 
the  last  week  of  August,  and  the  planet  will 
then  be  about  as  brilliant  as  it  ever  appears, 
and  will  be  very  favorably  situated  for  ob- 
servation in  the  constellation  Pisces.  We 
shall  then  see  Mars  in  the  flame-like  phase 
of  his  beauty,  and  he  will  dominate  the  eve- 
ning sky  during  the  whole  of  that  summer. 
At  oppositions  such  as  this  one  Mars  is  more 
favorably  situated  for  observation  from  the 
earth  than  any  other  heavenly  body  except 
the  moon. 

The  next  oppositions  will  take  place  the 
last  week  in  October,  1926,  in  December, 
160 


MARS 

1928,  January,  1931,  early  March,  1935,  the 
middle  of  May,  1937;  and  then  we  will  have 
two  more  splendidly  brilliant  oppositions  in 
July,  1939,  and  early  October,  1941,  respec- 
tively. 

During  the  years  that  Mars  does  not  ap- 
pear in  the  evening  we  need  not  be  deprived 
of  a  sight  of  the  planet  if  we  will  look  for 
it  in  the  morning  sky.  A  few  months  after 
conjunction  it  may  be  seen  as  a  morning 
star,  rising  shortly  before  the  sun.  It  rises 
earlier  each  morning,  and  hence  can  be  seen 
each  morning  for  a  longer  time.  After  its 
hour  of  rising  has  reached  midnight  it 
then  passes  into  the  evening  sky  and  rises 
earlier  each  evening  until  it  reaches  [oppo- 
sition. 

The  movement  of  Mars  among  the  stars, 
as  we  see  it,  is  generally  toward  the  east,  and 
we  can  see  by  looking  that  it  changes  its 
place  among  the  constellations  in  that  di- 
rection, going  from  Aries  to  Taurus,  from 
Taurus  to  Gemini,  and  so  on.  On  each 
side  of  opposition,  however,  the  planet  ap- 
pears for  a  few  weeks  to  be  moving  west- 
ward among  the  stars.  This  is  the  retro- 
grade motion  which  an  outer  planet  appears 
to  have  when  we  are  overtaking  and  passing 
161 


THE    WAYS    OF    THE    PLANETS 

it,  and  which  has  been  explained  in  the  chap- 
ters on  the  movements  of  the  planets. 

SIZE,    ATMOSPHERE,    AND     TEMPERATURE 

In  size  Mars  is  one  of  the  smallest  mem- 
bers of  our  solar  family.  Its  mass  is  a  little 
more  than  one-ninth  that  of  the  earth,  and 
its  entire  surface  is  only  about  one-third  as 
great  as  ours.  It  is  the  merest  trifle  more 
dense  than  Mercury,  but  only  about  sixty- 
six  one-hundredths  as  dense  as  the  earth. 
Its  force  of  gravity  is  about  thirty-six  one- 
hundredths  as  powerful  as  that  of  the  earth. 
A  man  weighing  two  hundred  pounds  here 
would  be  relieved  of  about  one  hundred  and 
twenty-four  pounds  of  his  weight  if  trans- 
ported to  Mars,  weighing  there  only  seventy- 
six  pounds,  which  would  greatly  increase  his 
efficiency  if  he  were  in  other  respects  the 
same. 

It  would  necessarily  follow  that  Mars, 
having  such  small  force  of  gravity,  could  not 
long  retain  a  heavy  atmosphere,  even  if  it 
had  set  out  with  such  a  one.  No  molecule 
of  gas  moving  at  a  greater  speed  than  three 
and  thirteen-hundredths  miles  a  second  could 
be  held  by  Mars  in  its  atmosphere,  and  so 
162 


MARS 

much  as  it  may  have  had  of  the  rarer  gases 
which  move  with  great  rapidity  must  have 
escaped  long  ago.  But  it  did  not  begin  life 
with  an  atmosphere  heavy  in  proportion  to 
that  which  the  larger  planets  have.  We 
have  seen,  in  the  case  of  Mercury,  that  being 
one  of  the  small  planets  entails  many  re- 
strictions in  development.  Such  planets  not 
only  lose  their  atmosphere  more  quickly  than 
the  larger  ones,  but  it  is  less  dense  to  begin 
with.  The  atmosphere  of  Mars  is  probably 
no  denser  than  we  have  at  the  tops  of  our 
highest  mountains,  more  than  likely  not 
even  so  dense  as  that.  There  is  some  water 
vapor,  and  there  are  a  few  clouds  most  of 
the  time;  but  in  the  main  the  atmosphere 
is  so  clear  and  thin  that  we  can  without  any 
doubt  see  the  actual  surface  of  the  planet. 
It  is  not  certain  that  the  clouds  we  see  are 
formed  from  water  vapor,  as  clouds  of  the 
ordinary  kind  are.  It  has  been  suggested 
that  they  may  be  simply  dust-clouds.  But 
this  is  as  yet  not  much  more  than  a  sugges- 
tion, and  nothing  convincing  has  been  offered 
to  substantiate  the  idea.  Even  dust-clouds 
would  need  currents  of  air  to  create  and 
carry  them;  so,  whether  dust  or  vapor,  the 
presence  of  clouds  implies  an  atmosphere. 
12  163 


THE    WAYS    OF    THE    PLANETS 

The  famous  white  polar  caps,  which  fur- 
nish so  many  news  items  to  the  journals, 
are  also  of  uncertain  origin,  and  their  true 
nature  can  be  determined  only  by  a  fuller 
knowledge  of  the  atmosphere  of  Mars. 
They  appear  in  the  winter  season  on  the 
planet  and  disappear  in  its  summer,  so  there 
seems  to  be  no  doubt  that  they  are  dependent 
in  some  way  on  the  temperature  in  the  polar 
regions  of  Mars.  If  they  are  hoar-frost  or 
snow,  they  are  condensations  of  water  vapor; 
and,  in  that  case,  when  they  disappear  there 
must  be  sufficient  heat  to  melt  them.  It  has 
been  contended  that  the  sun's  rays  fall  too 
obliquely  on  the  poles  of  Mars  to  melt  more 
than  a  few  inches  of  snow,  but  that  the 
caps  may  be  light  snow  or  frost,  and  thus 
capable  of  being  dissolved  by  even  such 
oblique  rays  of  sunlight  as  they  receive. 
Also  it  has  been  suggested  that  the  deposit 
resembling  snow  may  be  carbon  dioxide, 
which  condenses  into  a  white  substance  at 
a  temperature  more  than  a  hundred  degrees 
( — 109°  Fahr.)  lower  than  is  necessary  to 
produce  snow  and  melts  at  a  correspond- 
ingly low  temperature.  What  the  nature  of 
the  phenomenon  seen  at  the  poles  of  Mars 
is  depends  largely  upon  what  the  tempera- 
164 


MARS 

ture  is;  and  the  temperature  in  turn  is  de- 
pendent in  some  measure  on  the  density  and 
constitution  of  the  atmosphere,  as  well  as 
the  planet's  distance  from  the  sun. 

The  normal  temperature  of  an  unprotected 
body  at  the  distance  of  Mars  from  the  sun 
is  about  thirty-two  degrees  blow  zero  (Fah- 
renheit) ;  and  since  we  know  Mars  has  no 
dense  atmosphere  to  retain  the  heat  ic  ac- 
quires, it  is  natural  to  suppose  the  existence 
there  of  a  very  low  temperature,  and  one 
incompatible  with  our  ideas  of  life  and 
growth.  The  most  favorable  conclusions  do 
not  place  the  mean  temperature  higher  than 
forty-eight  degrees  Fahrenheit.  It  is  cer- 
tain that  the  planet  must  be  subjected  to 
great  extremes  of  temperature  within  its 
range,  since  its  filmy  robe  of  atmosphere  can- 
not protect  it  to  any  extent  from  the  direct 
rays  of  the  sun  during  the  day,  nor  prevent 
the  heat  from  escaping  with  great  rapidity 
at  night ;  so  that,  whatever  heat  it  may  gain 
in  the  daytime,  it  probably  loses  much  of  it 
during  the  night.  Until  we  know  more  of 
the  constitution  of  the  atmosphere  of  Mars 
we  can  know  nothing  certainly  about  its 
temperature  beyond  the  fact  that  it  is  much 
colder  than  ours  and  more  subject  to  varia- 

165 


THE    WAYS    OF    THE    PLANETS 

tions.  Anything  much  more  definite  than 
this  is  speculative  at  present.  But  with  all 
the  observation  that  is  now  given  to  Mars, 
and  with  the  always  increasing  facilities  for 
the  work,  many  uncertainties  regarding  the 
planet  are  likely  to  be  made  clear  before 
long.  The  spectroscope  will  probably  be 
the  final  resort  for  facts  concerning  the 
atmosphere. 

DISTANCE   AND   BRILLIANCY 

Mars  is,  on  an  average,  about  one  and  a 
half  times  farther  from  the  sun  than  we  are. 
Its  mean  distance  is,  in  round  numbers, 
one  hundred  and  forty-one  million  miles; 
but,  since  its  orbit  is  very  eccentric — more 
eccentric  than  that  of  any  other  of  the 
planets  except  Mercury — its  distance  from 
the  sun  varies  as  much  as  twenty-six  million 
miles.  At  its  nearest  the  planet  is  a  little 
more  than  one  hundred  and  twenty-eight 
million  miles  from  the  sun.  Its  greatest  dis- 
tance from  that  luminary  is  one  hundred  and 
fifty-four  million  miles.  At  its  mean  dis- 
tance something  more  than  twelve  and  a 
half  minutes  are  required  for  light  to  travel 
from  the  sun  to  the  planet. 
1 66 


MARS 

The  sun  becomes  quite  a  medium-sized 
object  as  viewed  from  Mars,  and  must  lose 
some  of  the  majesty  of  aspect  that  it  has 
to  us.  Its  apparent  diameter  is  about 
twenty-one  minutes,  which  would  make  it 
less  than  two- thirds  as  large  as  we  see  it. 
The  average  amount  of  light  and  heat  that 
it  furnishes  to  that  poor,  lightly  clad  little 
planet  is  less  than  half  as  much  as  we  re- 
ceive, though  when  the  planet  is  at  perihelion 
the  sun's  radiance  is  forty  per  cent,  more 
powerful  than  when  it  is  at  its  greatest 
distance  from  the  source  of  these  life-giving 
forces. 

The  eccentricity  of  the  orbit  of  Mars  is 
the  cause  also  of  his  great  variations  in 
distance  from  us,  and  hence  of  his  extreme 
changes  in  brilliancy.  These  changes  are 
many  times  greater  with  reference  to  the 
earth  than  to  the  sun.  At  the  planet's  near- 
est approach  to  us  it  comes  a  little  nearer 
than  thirty-five  millions  of  miles.  This  is 
when  it  is  in  opposition  in  August.  When 
opposition  occurs  in  February,  it  is  as  much 
as  sixty- two  millions  of  miles  from  us;  and 
when  it  is  in  conjunction,  and  on  the  other 
side  of  the  sun  from  us,  it  is  sometimes  two 
hundred  and  forty-eight  million  miles  dis- 
167 


THE    WAYS    OF    THE    PLANETS 

tant.  At  his  nearest  approach  light  leaps 
over  to  us  from  Mars  in  about  four  minutes 
and  eighteen  seconds;  at  his  greatest  distance 
it  cannot  reach  us  in  less  than  twenty-two 
minutes.  The  apparent  mean  diameter  of 
Mars  is  about  nine  and  fifty-six  hundredths 
seconds,  but  varies  from  three  and  six-tenths 
seconds,  when  the  planet  is  farthest  away, 
to  twenty-five  seconds  when  it  is  nearest 
to  us. 

While  Mars  does  not  exhibit  the  phases 
of  the  inner  planets  Venus  and  Mercury, 
by  showing  a  disc  sometimes  at  half -full  and 
sometimes  at  crescent  it  is  sufficiently  near 
us  to  be,  in  certain  positions,  gibbous,  or  to 
show  a  little  less  than  a  full  face.  When 
this  occurs  Mars  is  about  half-way  between 
opposition  and  conjunction,  and  the  earth  and 
the  sun  are  so  situated  that  we  are  slightly 
to  one  side  of  the  fully  illuminated  face  of 
Mars.  This  phase,  however,  is  not  sufficient- 
ly marked  to  make  any  material  difference 
in  the  brilliancy  of  the  planet.  It  is  not 
apparent  without  the  aid  of  a  telescope. 

From  Mars  the  earth  shows  all  the  phases 

that  Venus   shows  to  us.     When  Mars  is 

flaming  down  upon  us  in  his  position  of 

greatest  brilliancy  we  present  to  him  a  thin 

168 


MARS 

crescent.  When  he  sees  our  full  face  we 
are  on  the  opposite  side  of  the  sun  from  him. 
It  would  be  necessary  to  have  a  more  bril- 
liant electrical  illumination  than  any  we 
have  yet  seen  to  lighten  the  dark  side  of  the 


MARS:  DIFFERENCE  IN  ITS  APPARENT  SIZE  AT  ITS  NEAREST, 
MIDDLE,  AND  FARTHEST  DISTANCE  FROM  THE  EARTH 

Mars  appears  fifty  times  brighter  when  nearest  than  when  farthest 
away. 


earth  and  exchange  signals  with  Mars 
when  we  are  nearest  to  him — if,  indeed,  our 
atmosphere  would  permit  from  Mars  any 
view  at  all  of  the  surface  of  the  earth,  which 
is  not  at  all  certain.  In  spite  of  its  phases, 
the  earth  must  shine  on  Mars  at  times  in 
a  very  attractive  way.  It  is  not  so  bright, 
perhaps,  as  Venus  is  to  us,  nor  as  we  are  to 
Venus;  but  with  our  moon  circling  about 
us  we  may  well  be,  when  in  a  favorable 
169 


THE    WAYS    OF    THE    PLANETS 

situation,  a  very  interesting  double  star,  the 
distance  between  earth  and  moon  appearing 
on  Mars  about  equal  to  one-fourth  of  the 
apparent  diameter  of  the  moon. 

DAY  AND  NIGHT,  AND  SEASONS 

Owing  to  the  undoubted  permanent  mark- 
ings on  the  surface  of  Mars,  astronomers 
have  been  able  to  determine  the  length  of 
its  day  with  much  less  likelihood  of  error 
than  in  the  case  of  any  other  planet  except 
the  one  on  which  we  dwell.  It  rotates  on  its 
axis  in  twenty-four  hours,  thirty-seven  min- 
utes, and  twenty- three  seconds,  which  makes 
its  day  nearly  forty  minutes  longer  than  ours. 
In  our  greed  for  all  too  fleeting  time  we 
may  feel  a  little  envy  of  these  extra  minutes, 
which  would  mean  so  much  to  us  if  added  to 
our  day.  But  they  do  not  seem  so  important 
when  we  consider  that  while  Mars  is  having 
six  hundred  and  seventy  of  these  days  we 
are  having  six  hundred  and  eighty-seven  of 
ours,  which,  after  all,  seems  to  give  us  eigh- 
teen days  more  of  time.  Our  attitude  tow- 
ard the  situation  depends  upon  the  point  of 
view. 

The  axis  of  Mars  is  inclined  to  its  orbit 
170 


MARS 

about  twenty-four  degrees  and  fifty  minutes. 
This  is  but  little  more  than  the  inclination 
of  the  earth's  axis,  which  is  twenty-three 
degrees  and  twenty-seven  minutes.  Mars, 
therefore,  has  seasons  very  much  like  ours. 
They  are,  however,  slightly  more  marked 
than  ours,  because  of  the  somewhat  greater 
inclination  of  the  axis  of  the  planet;  and 
they  are  nearly  double  the  length  of  ours, 
because  it  takes  Mars  nearly  two  of  our 
years  to  make  its  journey  around  the  sun. 
Its  seasons,  then,  are  nearly  six  months 
long,  while  ours  are  but  three.  It  has  frigid, 
temperate,  and  torrid  zones,  practically  the 
same  as  the  earth  has.  Its  greatest  inequali- 
ties of  season  are  caused  by  the  eccentricity 
of  its  orbit.  It  is,  like  the  earth,  farthest  away 
from  the  sun  when  it  is  summer  in  the  north- 
ern hemisphere ;  and  in  this  situation  it 
travels  so  much  more  slowly  than  when  it  is 
near  the  sun  that  summer  in  its  northern 
hemisphere  is  seventy-five  days  longer  than 
the  same  season  in  the  southern  hemisphere. 
The  northern  summer  and  the  southern 
winter  are  each  three  hundred  and  eighty 
days  long,  while  the  reverse  seasons  in  each 
hemisphere  are  only  three  hundred  and  six 
days  long.  The  northern  summer  is  not 
171 


THE    WAYS    OF    THE    PLANETS 

only  longer  but  also  cooler  than  the  southern, 
and  the  northern  winter  is  shorter  and  warmer 
than  the  southern.  Which  hemisphere  has 
the  more  favorable  climate  depends  upon 
what  is  needed  on  Mars  to  maintain  life.  It 
may  be  that  in  this  regard  the  shorter,  hotter, 
southern  summer  is  the  best  season  the 
planet  affords. 

SURFACE   ASPECTS   OF   MARS 

Seen  through  a  telescope,  Mars  is  not  so 
red  as  it  appears  to  the  naked  eye.  One  of 
the  best  observers  of  it  has  compared  it  to 
an  opal,  and  it  surely  has  some  of  the  quali- 
ties of  an  opal  in  the  diversity  of  aspect  that 
it  shows  to  different  observers  from  different 
points  of  view.  No  other  planet  has  been  so 
subjected  to  controversy  over  what  appears 
on  its  surface.  This  is  partly  due  to  its  be- 
ing the  only  planet  whose  surface  is  without 
doubt  open  to  our  view  and  in  a  situation 
where  it  can  be  minutely  studied,  and  partly 
to  the  fact  that  the  controversy  involves 
questions  concerning  life  and  intelligence, 
which  are  always  of  intense  human  interest. 
Matters  of  this  vital  sort  are  never  accepted 
without  dispute.  That  is  one  way  of  getting 
172 


MARS 

at  the  truth.  In  the  intensity  of  the  dis- 
cussion the  question  of  the  existence  of  the 
phenomena  and  that  of  the  meaning  ascribed 
to  them  are  sometimes  unnecessarily  made 
to  depend  upon  each  other.  In  the  case  of 
Mars  it  may  well  be  that  there  is  less  differ- 
ence of  opinion  as  to  what  is  really  seen  on 
its  surface  than  as  to  the  meaning  of  the 
phenomena. 

There  are  recorded  observations  made  of 
Mars  as  early  as  272  B.C.,  more  than  two 
thousand  years  ago,  and  it  has  been  neariy 
two  hundred  and  fifty  years  since  the  snow- 
caps  were  first  seen.  Through  the  telescope 
not  only  the  snow-caps  are  plainly  visible  at 
the  proper  seasons,  but  there  are  also  visible 
dark  patches  over  the  surface,  showing  a 
variety  of  color,  and  in  certain  parts  changing 
somewhat  as  the  seasons  change.  It  is  one 
of  these  patches,  the  outline  of  which  sug- 
gests a  somewhat  twisted  eye,  that  is  known 
as  the  "eye  of  Mars."  The  main  surface 
of  the  planet  is  reddish  yellow  in  color; 
the  patches  on  it  are  variously  described  as 
gray,  grayish  green,  or  blue,  colors  which  in 
combination  could  easily  take  on  a  tone  of 
any  of  them  according  to  the  eye  of  the  ob- 
server, and  this  portion  of  the  planet's  sur- 


THE    WAYS    OF    THE    PLANETS 

face  does,  in  fact,  show  first  one  and  then 
the  other  of  them  predominating. 

When  the  planet's  differences  of  color  were 
first  observed,  the  reddish-yellow  portion 
was  supposed  to  be  land,  and  the  areas  of 
varying  bluish-green  and  gray  were  thought 
to  be  the  waters  of  the  ever-changing  seas. 
A  little  after  the  middle  of  the  last  century 
some  keen  eyes  saw  a  few  streaks  or  mark- 
ings of  some  sort  across  the  land  areas,  and 
in  1877  a  close  study  of  the  planet  by  an 
eminent  Italian  astronomer,  Schiaparelli, 
brought  to  his  view  many  greenish  streaks, 
all  directed  toward  the  so-called  seas,  and 
sometimes  seeming  to  intersect  there.  In 
publishing  this  discovery  Schiaparelli  called 
these  streaks  canalli,  which  is  properly  trans- 
lated "channels,"  but  appeared  in  English  as 
' '  canals . ' '  Since  * '  canal ' '  with  us  means  arti- 
ficially constructed  waterways,  the  discovery 
became  at  once  one  of  universal  interest ;  for 
artificial  waterways  mean  human  beings  to 
construct  them,  and  it  was  an  intensely  in- 
teresting thing  to  know  that  Mars  was  prob- 
ably inhabited  with  beings  at  least  somewhat 
after  our  own  kind.  It  was  a  new  world. 
The  little  planet  became  a  topic  of  absorb- 
ing interest  to  all  of  us.  And  thus  began  the 
174 


MARS 

controversy  over  the  habit  ability  of  Mars, 
and  the  meaning  of  its  surface  features,  in 
which  astronomers,  seeking  only  for  the 
truth,  have  taken  a  much  more  dignified 
part  than  they  have  sometimes  been  more  or 
less  sensationally  represented  as  doing.  The 
discoverer  of  the  so-called  canals  himself 
believed  them  to  be  natural  waterways  cut- 
ting through  the  land  after  the  manner  of 
our  straits  and  channels,  and  had  very  little 
to  say  in  explanation  of  them.  But  his  work 
gave  a  new  impetus  to  the  study  of  this  lit- 
tle brother  world  of  ours. 

In  our  own  country  the  observatory  at 
Flagstaff  is  the  one  the  best  known  among 
those  doing  research  work  on  Mars;  but  it  is 
not  the  only  one.  The  observatory  there  is 
finely  situated  in  the  thin,  clear  atmosphere 
of  Arizona,  the  mechanical  facilities  for  such 
work  are  good,  and  there  seems  no  doubt  that 
there  are  there  some  observers  who  have 
eyes  that  were  made  for  seeing.  All  that 
the  sharp  vision  of  Schiaparelli  saw  has 
been  seen  there,  and  much  more.  Several 
hundred  canals  have  been  discovered,  and 
at  certain  seasons  many  of  them  have 
appeared  to  become  double.  Their  courses 
have  been  followed,  and  their  appearances 


THE    WAYS    OF    THE    PLANETS 

and  disappearances  have  been  watched. 
Somewhere  near  six  hundred  of  them  have 
been  mapped.  According  to  these  maps, 
the  canals  seem  to  be  laid  out  with  a  geo- 
metrical precision  such  as  nature  is  not 
likely  to  follow;  they  run  across  some  regions 
that  were  formerly  supposed  to  be  water, 
and  they  have  points  of  convergence  every 
here  and  there,  forming  at  such  points  large 
dark  areas. 

Naturally,  when  a  person  has  discovered 
any  new  and  curious  phenomenon  in  nature 
he  seeks  to  determine  the  exact  meaning  of 
it.  It  would  have  very  little  interest  for 
him  if  he  did  not,  and  it  would  be  a  dry  lot 
of  facts  that  did  not  arouse  a  desire  to  do 
this.  The  interpretation  put  upon  what  has 
been  seen  at  the  observatory  at  Flagstaff  is,  in 
brief,  about  as  follows: 

The  surface  of  Mars  has  no  oceans  or 
moun tains.  The  reddish  areas,  which  form 
the  larger  part  of  the  surface,  are  deserts. 
The  blue-green  streaks  are  ribbons  of  vege- 
tation along  each  side  of  artificially  con- 
structed waterways,  which  are  of  immense 
length  and  cross  and  recross  each  other 
until  they  somewhat  resemble  a  network  of 
lines  over  the  desert  surface  of  the  planet, 
176 


MARS 

and  are  used  for  irrigating  this  arid  region. 
The  points  where  the  canals  converge  and 
form  the  large  dark  spots  are  oases  made 
by  the  water  carried  by  the  canals.  The 
water  is  supplied  by  the  melting  of  the  caps 
of  snow  at  the  poles  during  the  Martian 
summer,  the  expanding  of  the  lines  of  vege- 
tation seeming  to  occur  at  periods  corre- 
sponding to  the  time  required  for  the  water 
of  the  melting  snow  to  reach  the  oases. 
The  presence  of  this  vast  system  of  artificial 
waterways  covering  a  large  part  of  the  sur- 
face of  Mars  makes  it  seem  probable  that 
"Mars  is  inhabited  by  beings  of  some  sort 
or  other,"  that  these  beings  are  not  men 
such  as  we  know  anything  about,  but  that 
"there  may  be  a  local  intelligence  equal  to 
or  superior  to  ours." 

These  conclusions  concerning  what  is  seen 
on  Mars  are  not  held  by  any  one  to  be  com- 
pletely proved,  but  are  thought  by  their  au- 
thor to  follow  reasonably  from  the  phenom- 
ena as  observed.  By  persons  of  a  different 
temperament  they  are  regarded  as  too  com- 
plete an  explanation,  particularly  as  the 
data  upon  which  they  are  founded  are  not 
undisputed.  Some  of  the  best  astronomers 
have  not  been  able  even  to  see  the  multitude 
177 


THE    WAYS    OF    THE    PLANETS 

of  fine  lines,  much  less  to  give  any  explana- 
tion of  them.  Others  do  not  regard  it  as 
certain  that  they  are  so  geometric  in  their 
outlines  as  to  suggest  anything  more  than 
cracks  or  clefts  in  the  surface  of  Mars,  such 
as  might  be  made  by  nature,  and  consider 
that,  instead  of  indicating  life,  human  or 
other,  they  may  be  the  marks  of  age,  such 
as  similar  lines  or  cracks  which  have  been 
observed  on  Mercury  seem  to  be. 

Also,  it  is  not  at  all  certain  that  there  is 
sufficient  water  vapor  in  the  slight  atmos- 
phere of  Mars  to  furnish  the  snow  necessary 
for  this  great  irrigating  system,  nor  the  heat 
to  melt  it  at  the  proper  season.  The  natural 
temperature  of  Mars  would  be,  as  we  have 
seen,  very  low,  and  unless  it  is  modified  in 
some  way  not  yet  indicated  everything  points 
to  a  frigidity  too  intense  to  permit  the  con- 
tinuance of  life  and  growth  of  any  sort 
known  to  us. 

These  things  must  all  be  reckoned  with 
before  anything  certain  can  be  known  of  the 
surface  of  Mars.  The  difficulty  of  pro- 
nouncing upon  the  minute  details  is  impres- 
sively indicated  by  Professor  Moulton,  who 
says  that,  even  under  the  finest  conditions 
and  with  the  best  telescopes,  it  is  like  view- 
178 


MARS 

ing  "a  perfectly  accurate  relief  map  of  the 
whole  United  States  made  on  such  a  scale 
that  it  would  be  only  three  inches  in  diam- 
eter and  held  at  a  distance  of  three  feet 
from  the  eye."  Under  such  a  near  limit  of 
vision,  we  can  well  see  that  differences  of 
opinion  might  arise. 

The  mere  fact  that  some  astronomers  have 
not  seen  the  lines  on  Mars  does  not  mean 
that  they  deny  their  existence.  Some  eyes 
have  greater  defining  power  than  others,  as 
well  as  some  telescopes,  as  every  one  knows. 
But  while  all  the  lines  and  patches  of  color 
that  are  claimed  to  have  been  seen  on  Mars 
doubtless  have  been  seen  by  some  persons, 
yet  it  is  not  necessary  to  accept  the  inter- 
pretation of  them  given  by  lively-minded 
observers  when  it  is  not  convincing.  There 
may  be  vegetation  on  Mars,  and  even  intelli- 
gent beings.  We  do  not  know;  and  thus  far 
there  is  not  much  to  support,  even  by  infer- 
ence, the  view  that  there  are.  If  we  want 
the  truth,  we  are  brought  no  nearer  to  it  by 
giving  full  credence  to  a  speculative  theory 
simply  because  it  is  interesting  and  pleas- 
ant; and  thus  far  all  theories  advanced  as  to 
the  nature  of  the  surface  markings  on  Mars 
are  speculations,  though  there  is  no  doubt  that 

13  179 


THE    WAYS    OF    THE    PLANETS 

the  marks  are  there.  It  is  pleasing,  how- 
ever, to  contemplate  the  idea  of  there  being 
on  Mars,  or  on  any  other  planet,  an  active 
intelligence  of  any  sort  resembling  what  we 
have  here  on  earth,  and  it  is  not  strange  that 
such  a  wide-spread  popular  interest  should 
attach  to  Mars,  in  view  of  what  has  been 
suggested  by  the  markings  on  its  surface. 

THE   SATELLITES    OF   MARS 

Mars  has  a  little  family  of  two  moons. 
Tiny  little  bodies  they  are,  the  smallest  in 
the  solar  family  except,  perhaps,  an  occasion- 
al asteroid.  Neither  one  of  them  is  more 
than  ten  miles  in  diameter,  and  the  two  to- 
gether are  smaller  than  any  other  known 
satellite.  They  can  only  be  seen  when  Mars 
is  in  opposition,  and  then  only  with  a  fairly 
large  telescope.  They  were  discovered  in 
1877,  and  named  Phobos  and  Deimos,  the 
names  of  the  two  attendants  of  the  god  of 
war.  Phobos  is  the  brighter  and  the  nearer 
to  the  planet.  It  is  less  than  four  thousand 
miles  from  the  surface  of  Mars;  and  on  ac- 
count of  its  being  so  near  and  the  shape  of 
Mars  being  a  spheroid,  like  that  of  the  earth, 
the  little  satellite  can  never  be  seen  from 
180 


MARS 

Mars  beyond  sixty-nine  degrees  of  latitude 
on  each  side  of  the  equator.  Within  these 
limits  it  shows  great  activity.  It  makes  a 
complete  circuit  around  Mars  in  seven  and 
a  half  hours;  and  this  swift  revolution,  com- 
bined with  the  motion  of  Mars  on  its  axis, 
makes  Phobos  seem  to  rise  in  the  west  and 
set  in  the  east,  pass  over  the  heavens  in  less 
than  twelve  hours,  and  go  through  all  its 
phases,  from  "new"  to  "full,"  one  and  a 
half  times  every  night.  Its  light  is  rather 
insignificant,  being  about  sixty  times  less 
than  we  receive  from  our  satellite;  but,  on 
the  whole,  it  must  be  a  rather  gay  and  pleas- 
ant little  moon. 

Deimos  is  not  any  larger  than  Phobos, 
and  not  as  bright ;  but  it  is  slightly  less  diffi- 
cult for  us  to  see,  because  it  is  between  two 
and  three  times  farther  away  from  Mars 
than  Phobos  is,  and  thus  not  so  much  lost 
in  the  light  of  the  planet.  It  circles  around 
Mars  in  a  little  more  than  thirty  hours,  and 
this,  being  only  six  hours  more  than  Mars 
consumes  in  turning  around  on  its  axis,  re- 
sults in  requiring  more  than  two  days  for 
the  satellite  to  pass  from  rising  to  setting. 
Between  rising  and  setting  it  goes  through 
its  phases  four  times.  It  can  be  seen  from 
181 


THE    WAYS    OF    THE    PLANETS 

all  parts  of  Mars,  but  gives  very  little  light 
to  the  planet — more  than  a  thousand  times 
less  than  our  moon  gives  us. 

The  symbol  of  Mars  is  $  ,  a  conventional- 
ized figure  representing  a  shield  and  a  spear 
— implements  of  war  appropriate  for  the  use 
of  the  deity  especially  connected  with  war- 
fare. 


XIII 

JUPITER 

ONE  never  feels  so  impressed  with  the 
power  of  the  sun  as  when  one  contem- 
plates it  in  relation  to  Jupiter.  Great 
Jupiter,  he  may  well  be  called,  nearly  five 
hundred  million  miles  out  in  space,  almost 
a  sun  himself,  the  center  of  a  system  con- 
taining bodies  larger  than  the  sun's  near- 
est planet,  Mercury;  and  yet  just  Jupiter, 
one  of  the  planets,  held  firmly  in  leash 
like  the  others  by  the  sun's  overwhelming 
force  of  gravity,  forever  compelled  to  revolve 
about  that  parent  body  with  the  rest  of  its 
offspring,  to  stay  at  home  within  the  bounds 
of  the  sun's  domain,  to  keep  within  certain 
limits  in  his  own  orbit,  forced  to  hasten  on 
when  he  comes  nearest  the  power  that  con- 
trols him,  and  unable  to  keep  up  the  same 
rate  of  speed  when  he  is  farther  away.  One 
may  well  wonder  at  the  immensity  beyond 
comprehension  of  the  stars,  among  which 
183 


THE    WAYS    OF    THE    PLANETS 

our  sun  is  but  a  very  small  one,  when  one 
considers  how  even  this  small  one  can  thus 
swing  huge  Jupiter  about.  For  Jupiter  is, 
after  the  sun  itself,  the  mammoth  member 
of  our  system.  In  volume  he  is  larger  than 
all  the  other  planets  put  together,  and  in 
mass  he  is  more  than  double  as  large  as  the 
combined  mass  of  all  the  others.  He  is  about 
equal  to  the  sun  in  density,  and  about  one- 
fourth  as  dense  as  the  earth. 

There  is  less  difference  in  size  between 
Jupiter  and  the  sun  than  there  is  between 
Jupiter  and  the  earth.  His  diameter  is 
eleven  times  greater  than  that  of  the  earth. 
The  sun's  diameter  is  only  ten  times  greater 
than  Jupiter's.  His  surface  is  one  hundred 
and  sixteen  times  that  of  the  earth;  the  sun's 
own  surface  is  only  a  hundred  times  larger 
than  his.  Jupiter  weighs  more  than  three 
hundred  times  as  much  as  the  earth;  the 
sun  weighs  only  six  times  more  than  Jupiter. 
At  the  equator  his  diameter  is  about  ninety 
thousand  miles;  but,  as  the  planet  is  much 
flattened  at  the  poles,  the  diameter  from 
pole  to  pole  is  only  a  little  more  than  eighty- 
four  thousand  miles.  This  flattening  is  due 
to  the  very  rapid  spinning  of  the  planet  on 
its  axis,  a  motion  that  will  always  cause  a 
184 


JUPITER,     THE     MAMMOTH     MEMBER     OF     THE     SOLAR     FAMILY — 
LARGER    THAN    ALL    THE    OTHER    PLANETS    PUT    TOGETHER 

This  photograph  shows  the  flattening    at   the  poles  and  also  the  belts 
encircling  the  planet.     It  was  photographed  at  the  Yerkes  Observatory. 


JUPITER 

plastic  body  to  bulge  at  the  equator,  and 
thus  flatten  at  the  poles. 

The  force  of  gravity  on  Jupiter  is  about 
two  and  one-half  times  greater  than  on  the 
earth.  A  fairy-like  figure  weighing  here  only 
a  hundred  pounds  would  be  held  to  the  sur- 
face of  Jupiter  with  a  force  equal  to  two 
hundred  and  sixty  pounds.  This  tremen- 
dous power  makes  Jupiter  the  greatest  dis- 
turbing body  among  all  the  planets.  He  gives 
Saturn  a  mighty  pull  when  the  two  planets 
come  near  each  other;  he  draws  some  of 
the  little  asteroids  five  or  six  degrees  out  of 
their  course  when  it  carries  them  into  the 
field  of  his  influence;  and  there  are  as  many 
as  thirty  comets  that  have  become  perma- 
nent members  of  the  solar  system,  because 
through  his  great  power  of  attraction  he  has 
made  them  captive. 

Jupiter  is  so  much  farther  from  the  sun 
than  we  are  that  his  orbit  is  about  five  times 
larger  than  that  of  the  earth.  In  conse- 
quence also  of  his  greater  distance  from  the 
sun,  he  moves  much  more  slowly  than  the 
earth.  His  average  velocity  is  about  eight 
miles  a  second.  It  requires  more  than  four 
thousand  days,  or  nearly  twelve  of  our  years, 
for  him  to  make  one  revolution  around  the 


THE    WAYS    OF    THE    PLANETS 

sun,  and  he  thus  consumes  more  than  ten 
thousand  of  his  own  days.  He  travels 
through  about  one  sign  of  the  zodiac  each 
year,  and  is  thus  not  very  difficult  to  keep 
trace  of,  since  the  signs  and  the  constella- 
tions of  the  zodiac  so  nearly  coincide.  His 
synodic  period,  or  the  period  from  one  op- 
position to  another,  is  a  fraction  less  than 
three  hundred  and  ninety-nine  days,  or  about 
one  year  and  a  little  more  than  a  month. 
His  daily  motion  in  the  skies  is  almost  too 
small  for  us  to  detect  it  without  observation 
for  more  than  a  day.  It  is  in  one  day  about 
equal  to  one-sixth  of  the  apparent  diameter 
of  the  moon;  but  in  a  month  he  has  moved 
a  distance  about  half  as  great  as  that  be- 
tween the  two  pointers  in  the  Big  Dipper, 
as  can  be  easily  seen  by  comparison  with  the 
stars  near  him. 

JUPITER'S  PLACE  IN  THE  SKY 

Jupiter  is  now  (1912)  in  the  constellation 
Scorpio,  and  he  will  be  in  this  region,  and 
thus  a  summer  star,  for  several  years  to 
come.  In  1913  he  will  be  in  opposition 
early  in  July,  and  will  then  be  in  Sagittarius, 
not  far  from  the  little  "milk  dipper,"  and 
186 


JUPITER 

will  be  a  gloriously  beautiful  object  during  all 
the  summer.  He  will  be  in  opposition  about 
August  10,  1914,  in  Capricornus,  and  will 
again  be  the  most  brilliant  object  in  the 
summer  sky.  In  1915  he  will  be  in  opposi- 
tion a  little  after  the  middle  of  September, 
and  will  then  be  situated  on  or  near  the 
eastern  edge  of  Aquarius,  where  he  will  be 
a  very  distinguished  star  during  all  the 
charming  evenings  of  late  summer  and  the 
autumn.  He  always  seems  particularly  splen- 
did when  in  this  season  of  the  year  he 
reaches  opposition.  The  insistent  brilliancy 
of  his  disc  brings  him  then  into  view  before 
the  sun  is  fairly  down ;  and  he  hangs,  placid 
and  alone,  in  the  southeastern  sky  during 
the  autumn  twilight,  and  later  in  the  eve- 
ning shows  to  advantage  his  dominating 
beauty,  with  Antares  on  the  west  of  him  and 
Fomalhaut  below  him,  no  less  charming  in 
their  own  way,  but  far  less  brilliant  than 
this  splendid  planet. 

•  In  1916,  when  opposition  will  occur  not 
far  from  Hallowe'en,  Jupiter  will  be  about 
on  the  eastern  border  of  the  constellation 
Pisces,  and,  rising  then  just  as  the  sun  sets, 
will  enliven  the  evening  view  for  the  rest 
of  that  year.  He  will  appear  at  his  very 
187 


THE    WAYS    OF    THE    PLANETS 

best  at  this  time,  for  he  will  be  at  about  his 
nearest  to  the  sun;  and  all  that  this  situation 
can  do  for  him  in  the  way  of  enhancing  his 
brilliancy  may  then  be  seen. 

In  1917  he  will  be  in  opposition  to  the  sun 
about  the  first  of  December,  in  Taurus ;  and  for 
the  next  few  years  he  will  be  a  winter  star,  mov- 
ing majestically  along  his  path  in  the  zodiac, 
never  more  than  one  and  a  half  degrees  from 
the  ecliptic,  and  passing  in  turn  the  Pleiades, 
Aldebaran,  Castor  and  Pollux,  and  the  lit- 
tle Bee-hive  in  Cancer.  There  will  be  no 
opposition  in  1918;  but  one  will  occur  early 
in  January,  1919,  when  Jupiter  is  in  the 
eastern  half  of  Gemini ;  and  toward  the  mid- 
dle of  February,  1920,  another  will  take 
place,  when  the  planet  is  in  Cancer,  with 
Castor  and  Pollux,  the  sparkling  twin  stars 
in  Gemini,  to  the  west  of  him. 

During  part  of  1920  and  all  of  the  next 
three  years  Jupiter  will  be  journeying  across 
Leo,  Virgo,  Libra,  and  Scorpio.  He  will  be 
opposite  the  sun  in  1921,  a  little  after  the 
middle  of  March;  in  1922,  in  the  latter  half 
of  April;  and  in  1923,  toward  the  very  last 
of  May.  He  will  pass  near  Regulus,  the 
sparkling  star  in  the  handle  of  the  Sickle, 
in  the  summer  of  1920;  near  Spica  in  1921; 
188 


JUPITER 

and  he  will  not  be  far  from  Antares  in 
1923. 

In  1924  Jupiter's  cycle  of  twelve  years 
will  be  completed,  and  he  will  be  in  opposi- 
tion again  early  in  July,  and  situated  near 
the  western  edge  of  Sagittarius,  not  far  from 
where  he  was  in  1912. 

These  cycles  do  not  repeat  themselves 
exactly ;  but  the  planet  lacks  only  four  days 
of  having  been  in  opposition  eleven  times 
during  twelve  of  our  years,  so  that  it  is  not 
difficult  to  keep  track  of  him  through  a  long 
series  of  years.  For  exact  dates,  such  as 
one  needs  in  a  very  close  study  of  the  planet, 
an  almanac  must  be  consulted;  but  this  is 
not  necessary  for  mere  recognition,  which 
is  all  that  is  needed  to  enjoy  the  acquaint- 
ance of  great  Jupiter. 

Every  year  Jupiter  is  an  evening  star  for 
more  than  six  months.  For  two  months 
before  opposition  he  rises  somewhat  after 
sundown;  at  opposition  he  appears  exactly 
at  the  setting  of  the  sun;  and  thereafter  he 
is  found  in  the  evening  sky,  appearing  far- 
ther toward  the  west  each  evening,  until, 
when  nearing  conjunction,  he  is  lost  to  our 
view  for  a  time.  He  is  a  morning  star  for 
an  equal  length  of  time,  and  fpr  about  three 
189 


THE    WAYS    OF    THE    PLANETS 

months  can  be  seen  between  midnight  and 
six  in  the  morning;  but  much  of  the  rest 
of }  the  time  he  is  obscured  by  the  day- 
light. 

Jupiter  retrogrades  in  his  motion  for  about 
two  months  before  and  after  each  opposition; 
but,  since  he  changes  his  place  to  the  extent 
of  only  two  and  a  half  degrees  a  month, 
the  whole  apparently  backward  movement 
amounts  only  to  ten  degrees  a  year.  Still,  it 
is  very  interesting  to  watch  him  swing  back 
and  forth  over  this  ten  degrees  before  he 
starts  out  on  each  yearly  journey. 

DISTANCE,    LIGHT,    AND   HEAT 

Jupiter  is  nearly  five  times  farther  from 
the  sun  than  we  are.  His  mean  distance 
from  that  orb  is  four  hundred  and  eighty- 
three  millions  of  miles.  His  orbit  is  not  so 
eccentric  as  that  of  Mercury  or  of  Mars, 
but  the  eccentricity  is  sufficient  to  make  his 
distance  vary  by  as  much  as  forty-two 
millions  of  miles.  His  distance  is  five  hun- 
dred and  four  millions  of  miles  when  he  is 
farthest  from  the  sun,  and  four  hundred  and 
sixty- two  millions  when  he  is  nearest  to  it. 
On  account  of  his  orbit  being  outside  of 
190 


JUPITER 

ours,  we  are  at  times  nearer  to  him  and  at 
others  farther  from  him  than  the  sun  ever 
is.  At  his  best  situation  when  in  opposition, 
we  are  three  hundred  and  sixty-nine  million 
miles  from  him.  This  is  more  than  ten 
times  farther  than  we  are  from  Mars  at  that 
planet's  most  favorable  oppositions,  and  yet 
Jupiter  is  much  brighter  at  such  times  than 
Mars  ever  appears  to  be.  At  the  times  of 
conjunction  he  is  five  hundred  and  ninety- 
six  millions  of  miles  from  us,  but  is  still 
always  brighter  than  a  first-magnitude  star 
like  Capella  or  Vega. 

Although  the  distance  of  Jupiter  from  us 
varies  thus  two  hundred  and  twenty-seven 
million  miles,  there  is  never  in  him  the 
marked  difference  in  brilliancy  that  we  see 
in  Mars.  He  is  at  all  times  so  far  away  that 
the  variation  in  distance  does  not  count  for 
as  much,  though  we  can  see  the  effect  of  it 
plainly  enough,  even  with  the  naked  eye. 
Light,  with  all  its  marvelous  speed,  consumes 
more  than  fifty-three  minutes  in  its  journey 
from  Jupiter  to  the  earth  when  we  are  most 
widely  separated  from  him.  When  we  are 
nearest  to  him  light  comes  to  us  from  the 
planet  in  twenty  minutes  less  time.  At  his 
average  distance  from  the  sun  it  requires 
191 


THE    WAYS    OF    THE    PLANETS 

about  forty-three  minutes  for  light  to  pass 
from  the  sun  to  Jupiter. 

Notwithstanding  the  sun's  great  power 
over  Jupiter  in  shaping  his  course,  it  does 
not  give  him  much  in  return  for  his  sub- 
serviency. So  far  as  light  and  brilliancy  are 
concerned,  it  is  to  Jupiter  a  very  small  sun 
indeed.  To  an  observer  on  Jupiter  the  sun 
would  not  appear  to  be  more  than  one-fifth 
as  large  as  it  seems  to  us.  The  light  it  fur- 
nishes to  Jupiter  is  twenty-five  times  less  than 
we  receive;  and  if  the  planet  depended  en- 
tirely upon  the  sun  for  heat,  his  temperature 
would  be  more  than  two  hundred  degrees 
below  zero,  Fahrenheit.  There  is  every 
reason  to  believe  that  the  little  heat  the  sun 
gives  to  this  mighty  planet  does  not  count 
for  much  one  way  or  the  other  at  the  planet's 
present  stage  of  development.  Jupiter  does 
not  need  the  nourishing  that  the  smaller 
terrestrial  planets  must  have,  or  die.  He  is 
probably  almost  a  sun  himself.  We  are  not 
at  all  certain  that  the  planet  is  even  so  far 
cooled  as  to  have  a  solid  surface.  If  it  has, 
there  is  reason  to  think  that  the  surface  is 
at  least  red  hot,  and  gives  to  the  planet  a 
temperature  higher  than  anything  we  have 
any  comprehension  of.  Jupiter's  atmos- 
192 


JUPITER 

phere,  too,  is  extremely  thick  and  dense,  so 
that  the  planet  is  probably  so  protected  that 
it  gets  very  little  heat  from  the  sun  and 
loses  very  little  of  its  own. 

It  is  certain,  however,  that  this  great 
planet  is  not  so  much  of  a  sun  as  to  shine 
by  its  own  light.  The  light  we  receive, 
though  it  is  very  brilliant,  is  reflected  sun- 
light. This  is  shown  by  the  fact  that  the 
planet  does  not  furnish  light  for  its  own 
satellites.  When  they  pass  into  its  shadow 
the  sunlight  is  shut  off  from  them;  and  if 
they  receive  any  light  from  Jupiter,  it  is  too 
dusky  to  be  perceptible  to  us.  That  the 
planet  may  have  a  red  glow,  though,  is 
also  suggested  by  the  action  of  the  satellites. 
When  they  pass  between  us  and  Jupiter 
they  sometimes  cast  less  of  a  shadow  on  his 
surface  than  would  be  expected,  thus  indi- 
cating that  the  surface  is  not  altogether 
dark,  though  it  may  only  dully  glow  rather 
than  shine. 

DAY  AND   NIGHT,    SEASONS,  AND   ATMOSPHERE 

Jupiter  accomplishes  one  rotation  in  a 
little  less  than  ten  hours;  but,  curiously 
enough,  all  parts  of  the  planet  do  not  rotate 


THE    WAYS    OF    THE    PLANETS 

in  the  same  length  of  time.  A  day  at  the 
equator  is  nine  hours  and  fifty  minutes  in 
length.  In  some  of  the  higher  latitudes  it 
is  nine  hours  and  fifty-five  minutes,  and 
this  notwithstanding  the  equator  is  so  much 
larger  in  circumference  than  any  other  part 
and  any  one  point  on  it  has  farther  to  go  in 
a  revolution.  As  many  as  eight  different 
rates  of  rotation  have  been  observed;  and 
even  in  the  same  zones  some  parts  seem  to 
lag  behind  others,  taking  a  little  more  time 
to  complete  the  rotation  than  other  parts 
surrounding  them.  This  is  another  indica- 
tion that  Jupiter  is  not  a  solid  body.  The 
surface  features  are  none  of  them  permanent, 
though  some  of  them  remain  practically  the 
same  for  years.  It  is  through  this  occa- 
sional stability  of  them  that  it  has  been 
possible  to  mark  the  planet's  time  of  rota- 
tion. 

In  the  matter  of  seasons  Jupiter  has  very 
little  variety.  The  axis  of  the  planet  is  in- 
clined but  little  more  than  three  degrees  to 
its  orbit,  so  that  whatever  amount  of  heat 
the  sun's  radiance  affords  must  be  very  nearly 
uniform  during  the  entire  Jovian  year.  Its 
distance,  too,  is  at  all  times  so  great  that 
there  would  be  no  appreciable  change  in  tem- 
194 


JUPITER 

perature  between  its  perihelion  and  aphelion 
positions. 

There  is  every  indication  that  Jupiter  has 
an  extraordinarily  dense  and  deep  atmos- 
phere. It  has  been  sometimes  estimated  to 
be  as  much  as  a  thousand  miles  in  depth, 
and  the  spectroscope  shows  it  to  be  heavily 
laden  with  vapor.  But  beyond  these  very 
general  facts  not  much  is  definitely  known 
about  it.  It  is  certain,  though,  that  it  is 
very  different  from  our  atmosphere.  The 
spectroscope  shows  in  it  elements,  or  com- 
pounds of  elements,  which  are  not  familiar 
to  us.  The  enormous  gravitative  power  of 
Jupiter  would  enable  him  to  hold  gases 
rarer  than  the  earth,  or  the  smaller  planets 
like  the  earth,  ever  acquired.  A  molecule  of 
gas  would  have  to  move  more  rapidly  than 
thirty-seven  miles  a  second  to  escape  from 
Jupiter.  The  earth,  as  we  have  seen,  can- 
not hold  any  gases  moving  faster  than  seven 
miles  a  second.  So  there  are  many  gases  which 
may  forever  remain  in  Jupiter's  atmosphere 
and  yet  have  never  had  a  place  in  ours. 

SURFACE   FEATURES 

Seen  through  a  telescope,  Jupiter  shows 
the  loveliest  variety  of  colors,  with  the  red- 
14  195 


THE    WAYS    OF    THE    PLANETS 

dish  ones  always  most  conspicuous.  The 
slightly  pink-tinted  steady  light  that  we  get 
from  the  planet  with  the  naked  eye  in  no 
way  suggests  the  turbulent,  flame-like  aspect 
that  a  telescopic  view  opens  to  us.  The 
telescope  also  reveals  very  clearly  that  flat- 
tening at  the  poles  which  has  already  been 
spoken  of. 

With  so  dense  an  atmosphere  as  Jupiter 
most  likely  has,  it  is  sometimes  doubtful 
whether  his  surface  can  be  seen  by  us  at 
all.  But  it  is  certain  that  we  see  something 
apparently  much  more  dense  and  stable 
than  an  atmosphere  is  supposed  to  be;  and 
hence  it  is  thought  that,  in  spite  of  its  thick- 
ness, the  atmosphere  may  be  only  partially 
opaque,  and  that  it  may  be  in  some  places 
even  more  or  less  transparent. 

It  does  not  seem  probable  that  the  mark- 
ings on  Jupiter  are  wholly  atmospheric. 
Some  of  them  indicate  that  the  substance 
we  see  has  considerably  more  consistency 
than  a  mere  gas.  The  whole  surface  of  the 
planet  is  covered  with  belts  and  spots  of 
various  colors  and  varying  shapes.  The 
belted  appearance  is  particularly  marked. 
It  has  been  noticed  for  more  than  two  hun- 
dred years,  and  can  be  seen  with  a  com- 
196 


JUPITER 

paratively  small  telescope.  Sometimes  as 
many  as  twenty  or  thirty  belts  have  been 
seen  at  one  time.  All  of  them  are  parallel 
with  the  equator. 

Two  broad  red  belts  on  each  side  of  the 
equator,  called  the  tropical  belts,  are  very 
distinct,  and  sometimes  retain  the  same 
shape  and  color  for  months  at  a  time,  though 
sometimes  they  change  rapidly  in  both  color 
and  outline.  Between  them  is  the  equa- 
torial belt,  which  is  also  a  semi-permanent 
feature,  remaining  often  for  a  considerable 
period  unchanged.  These  belts,  and  the 
spots  that  sometimes  appear  on  and  near 
them,  have  been  closely  watched,  because 
about  the  equator,  and  especially  just  south 
of  it,  is  the  region  of  greatest  activity  on 
Jupiter's  surface. 

One  feature  that  more  nearly  suggests 
solidity  and  permanency  than  anything  else 
on  Jupiter  is  the  famous  great  red  spot 
which  lies  in  the  southern  hemisphere  just 
below  the  southern  tropical  belt.  It  ap- 
peared about  thirty-five  years  ago,  in  July, 
1878,  as  a  pale  pink  spot,  grew  brighter  for 
two  or  three  years,  and  then  faded,  until, 
at  the  end  of  two  or  three  more  years,  it 
was  almost  invisible.  In  another  year  it 
197 


THE    WAYS    OF    THE    PLANETS 

came  again,  and  increased  in  brightness  for 
five  or  six  years.  Then  it  grew  a  little  fainter, 
and  has  since  remained  a  rather  faint  red 
spot,  but  plainly  visible. 

In  shape  the  great  red  spot  is  an  immense 
oval  as  much  as  thirty  thousand  miles  from 
east  to  west  and  seven  thousand  miles  from 
north  to  south,  which  gives  it  a  surface  four 
or  five  times  as  large  as  the  land  area  on 
the  entire  earth,  and  larger  even  than  the 
the  whole  surface  of  the  earth  including  the 
oceans.  Although  retaining  its  own  shape, 
it  seems  to  drift  about  among  its  surround- 
ings, showing  that  it  is  not  attached  to  any 
solid  surface;  and  yet  it  has  a  suggestion  of 
solidity  in  itself,  which  was  shown  when  it 
and  another  smaller  spot  were  seen  to  be 
drifting  toward  each  other,  and  then  finally 
to  meet.  Instead  of  colliding  or  going  over 
or  under,  they  clamly  drifted  to  one  side  and 
went  around  each  other. 

Appearances  such  as  this  have  suggested 
the  idea  that  the  great  spot  might  be  a  con- 
tinent in  process  of  formation.  Such  an 
idea  is  at  best  a  speculation;  but  it  would 
be  interesting  if  it  should  prove  that  we  are 
witnessing  on  Jupiter  the  process  through 
which  our  own  earth  must  at  one  time  have 
198 


JUPITER 

passed  when  its  crust  began  to  solidify  in 
patches,  as  one  of  the  steps  in  the  long  period 
of  evolution  which  has  prepared  it  for  our 
uses.  It  is  not  at  all  certain  that  Jupiter 
will  ever  be  just  like  the  earth.  The  differ- 
ences between  its  atmosphere  and  ours  may 
have  some  influence  in  its  development  that 
we  have  little  knowledge  of  at  present,  and 
there  are  some  other  fundamental  differences 
between  the  two  planets  which  may  in  some 
way  effect  a  difference  in  development.  But 
in  a  general  way  we  know  that  the  planet 
will  in  time  become  more  condensed  than  it 
now  is  and  will  finally  solidify.  Whether 
the  processes  will  be  carried  on  in  just  the 
same  way  in  which  they  have  been  here  on 
the  earth  is  not  so  certain. 

JUPITER'S  SYSTEM  OF  SATELLITES 

Jupiter  is  the  center  of  a  superb  system  of 
satellites,  eight  in  number.  Four  of  them 
were  first  seen  in  1610,  and  have  the  honor 
to  be  the  first  heavenly  bodies  discovered  by 
means  of  the  telescope.  The  fifth  one  was  not 
discovered  until  1892.  The  sixth  was  first  seen 
in  1904,  and  the  seventh  in  1905.  After  three 
years  an  eighth  was  discovered  (in  1908). 
199 


THE    WAYS    OF    THE    PLANETS 

When  the  first  four  satellites  were  dis- 
covered they  were  named  respectively,  in 
the  order  of  their  distances  from  Jupiter, 
lo,  Europa,  Ganymede,  and  Callisto.  Gany- 
mede is  not  only  the  largest  of  the  four,  but 
is  also  the  largest  satellite  in  the  solar  sys- 
tem. It  is  larger  than  Mercury,  and  not 
much  smaller  than  Mars.  Callisto  is  next 
to  Ganymede  in  size,  and  is  about  the  size 
of  Mercury.  lo  is  about  the  size  of  our 
moon,  and  Europa  is  not  much  smaller. 
Under  very  favorable  conditions  Ganymede 
and  Callisto  can  be  seen  by  the  naked  eye; 
but  a  good  many  persons  think  they  see  the 
moons  of  Jupiter  when  they  see  only  some 
small  stars  in  that  region.  They  are  in- 
visible to  most  people,  but  probably  could 
be  seen  oftener  if  it  were  not  for  the  glaring 
light  of  the  planet,  which  more  or  less  ob- 
scures anything  so  near  it. 

After  the  discovery  of  Jupiter's  fifth 
satellite,  astronomers  seem  to  have  become 
possessed  with  that  dull  spirit  of  orderliness 
such  as  is  sometimes  exhibited  by  city 
councils  in  substituting  numbers  for  historic 
and  beautiful  names  in  designating  streets. 
No  more  of  Jupiter's  satellites  were  given 
names  such  as  might  be  appropriate  for 
200 


JUPITER 

members  of  this  Jovian  family;  but  all  were 
given  numbers — the  first  four  in  order  of 
their  distance  from  Jupiter,  the -others  in 
order  of  their  discovery.  lo,  Europa,  Gany- 
mede, and  Callisto  are  now  designated,  re- 
spectively, I,  II,  III,  and  IV,  while  V,  VI, 
VII,  and  VIII  have  never  had  any  designa- 
tion other  than  these  numbers. 

The  fifth  satellite,  discovered  in  1892,  is 
the  nearest  to  Jupiter,  and  the  smallest  of 
all  his  satellites.  Its  diameter  is  probably 
not  more  than  one  hundred  and  twenty 
miles,  but  its  exact  size  can  be  estimated 
only  by  the  amount  of  light  it  reflects.  It 
is  too  small  to  show  a  measurable  disc,  and 
cannot  even  be  seen  when  it  makes  a  transit 
across  the  planet.  It  would  seem  then  a  mere 
speck,  if  we  could  see  it  at  all.  It  makes  one 
revolution  about  Jupiter  in  less  than  twelve 
hours  (eleven  hours  and  fifty-seven  minutes), 
and  is  only  a  little  more  than  twenty-two 
thousand  miles  from  the  surface  of  the  planet 
at  the  equator.  It  appears  to  us  as  a  star 
of  about  the  thirteenth  magnitude,  and  can- 
not be  seen  except  with  a  large  telescope. 
Owing  to  the  great  curvature  of  the  planet, 
and  to  the  satellite's  being  so  near  him,  it 
cannot  be  seen  from  the  surface  of  Jupiter 
201 


THE    WAYS    OF    THE    PLANETS 

beyond  sixty-five  degrees  of  latitude.  It 
moves  faster  than  any  other  satellite  in  the 
solar  system,  going  at  the  rate  of  sixteen  and 
a  half  miles  a  second.  It  does  not  make  a 
revolution  in  as  short  a  time  as  Phobos,  the 
little  satellite  of  Mars,  does,  but  it  has  a 
much  longer  distance  to  travel  and  goes  at 
a  faster  rate.  The  fact  that  Jupiter  rotates 
in  ten  hours  and  the  satellite  makes  a  revo- 
lution around  him  in  twelve  hours  results 
in  the  satellite's  taking  five  of  Jupiter's  days 
to  cross  from  the  eastern  horizon  to  the 
western.  It  would  go  through  all  its  phases 
four  times  during  that  period  if  it  were  not 
that,  being  so  near  the  planet,  his  huge  form 
cuts  off  the  sunlight  from  the  little  satellite 
for  nearly  one-fifth  of  the  time,  and  it  is 
never  seen  "full." 

This  satellite  is  very  difficult  for  us  to  see 
on  account  of  its  diminutive  size  and  its 
nearness  to  the  shining  disc  of  Jupiter;  yet 
it  was  discovered  by  means  of  the  telescope, 
and  not  by  photography,  as  so  many  small 
bodies  are  discovered  nowadays,  and  by  a 
man  who  thus  far  has  not  been  able  to  see 
the  fine  line  markings  on  Mars,  which  some 
other  astronomers  think  they  can  see — a 
fact  that  is  very  interesting  as  showing  the 

202 


JUPITER 

difference  between  observers  even  of  great 
keenness  of  vision.  From  this  satellite  Ju- 
piter would  seem  an  enormous  body,  nearly 
eighty-five  times  larger  than  our  sun  ap- 
pears to  us,  and,  no  doubt,  a  splendid  object. 
But  the  little  satellite  pays  rather  dearly  for 
the  view  by  suffering  numerous  and  long- 
continued  eclipses. 

The  sixth  and  seventh  satellites  are  also 
very  minute  bodies,  measuring  probably  less 
than  one  hundred  miles  in  diameter.  They 
circle  about  Jupiter  a,t  a  distance  nearly 
thirty  times  more  remote  'than  our  moon 
is  from  us.  They  are  about  seven  million 
miles  from  the  planet,  and  probably  not 
more  than  barely  visible  from  it.  It  takes 
them  two  hundred  and  sixty-five  days  to 
make  one  revolution,  which  is  more  than 
five  hundred  times  as  long  as  the  period  of 
Jupiter's  nearest  satellite.  These  two  satel- 
lites are  so  nearly  of  one  size  and  revolve 
so  nearly  in  the  same  time  and  at  the  same 
distance  from  Jupiter  that  they  are  thought 
to  have  had  a  common  origin.  Just  what 
their  relation  is  has  not  yet  been  determined. 

The  eighth  satellite,  discovered  in  January, 
1908,  is  certainly  no  larger,  and  is  perhaps 
still  more  tiny,  than  the  sixth  and  the  seventh, 
203 


THE    WAYS    OF    THE    PLANETS 

though  it  is  a  little  brighter  than  either  one 
of  them.  It  is  about  three  times  farther 
away  from  Jupiter  than  the  seventh  satel- 
lite, and  with  eyes  such  as  ours  would  not  be 
visible  from  Jupiter.  It  shows  to  us  as  about 
a  seventeenth-magnitude  star,  which  is  al- 
most at  the  limit  of  our  vision  with  even 
the  largest  telescope.  It  seems  to  revolve 
about  Jupiter  in  a  direction  exactly  opposite 
to  that  of  the  other  satellites — a  retrograde 
motion  that  appears  in  the  solar  system  in 
only  two  or  three  other  cases  and  has  not 
yet  been  entirely  accounted  for. 

Jupiter's  satellites  have  played  an  im- 
portant part  in  astronomical  discoveries 
and  investigations.  It  was  through  obser- 
vation of  their  transits  that  it  was  discovered 
that  light  occupied  time  in  passing  through 
space.  When  Jupiter  was  near  us  in  his 
orbit,  the  eclipses  occurred  too  soon  for  their 
calculated  time;  when  he  was  farther  away, 
they  occurred  too  late.  It  was  found  that 
these  irregularities  were  due  to  the  fact  that 
light  is  not  transmitted  through  space  in- 
stantaneously, and  further  investigation 
showed  that  it  travels  at  the  rate  of  186,400 
miles  a  second.  The  eclipses  of  Jupiter's 
moons  are  carefully  computed  and  recorded 


JUPITER 

in  the  Nautical  Almanac,  and  it  is  through 
observations  of  them  that  chronometers  are 
corrected  at  sea. 

Ganymede  and  Callisto  have  been  found 
to  keep  always  the  same  face  toward  the 
planet,  as  our  moon  keeps  always  the  same 
face  toward  us;  and  it  is  thought  that  all  of 
Jupiter's  satellites  probably  do  this. 

The  symbol  of  Jupiter  is  2£,  a  hieroglyph 
for  the  eagle,  which  was  the  bird  of  Jove. 


XIV 

SATURN 

AMONG  the  four  planets  that  we  com- 
monly see,  the  easiest,  perhaps,  to  keep 
track  of  is  Saturn.  Its  peculiar  aspect  is 
very  distinctly  marked.  It  appears  as  a 
large,  pale,  yellow  star  shining  with  a  soft, 
misty  light  that  sometimes  barely  escapes 
being  dull.  It  is  always  as  bright  as  a  first- 
magnitude  star,  but  not  always  as  bright 
as  Sirius,  and  never  as  brilliant  as  Mars, 
Jupiter,  or  Venus  when  they  are  at  their 
brightest.  The  general  effect  of  it  is  as  a 
large  rather  than  a  brilliant  star. 

The  only  time  it  loses  these  very  marked 
characteristics  is  when  it  is  drawing  in  tow- 
ard the  sun,  and  thus  nearing  conjunction. 
At  such  times  we  see  it  each  evening  lower 
in  the  rosy  glow  of  the  setting  sun,  and  more 
and  more  obscured  and  changed  in  color  by 
the  surrounding  atmosphere.  Then  it  some- 
times seems  as  red  as  Mercury,  and  some- 
206 


SATURN 

times  even  twinkles  a  little  in  a  sort  of  fare- 
well gaiety  as  it  backs  away  from  us  into 
the  rays  of  the  dazzling  sun  and  finally  dis- 
appears for  a  time  from  the  evening  sky. 
Proximity  to  the  sun  and  entanglement  in 
the  atmosphere  of  the  horizon  has  this  effect 
more  or  less  on  all  the  planets,  as  we  know, 
but  it  always  seems  unexpected  in  Saturn, 
because  it  is  so  out  of  keeping  with  his 
ordinarily  large,  pale,  placid  face,  which  sug- 
gests softness  and  gentleness  rather  than 
vivacity. 

But  there  is  no  mistaking  the  planet  even 
under  this  aspect  if  we  but  stop  to  think  where 
he  is.  And  it  is  through  knowing  where  he 
is  that  it  is  so  easy  to  keep  track  of  Saturn. 
For  nearly  two  years  and  a  half,  on  an  aver- 
age, he  remains  in  the  same  constellation, 
passing  slowly  over  about  one  degree  a 
month,  or  a  little  more  than  twelve  degrees 
in  a  year,  occupying  almost  thirty  years  in 
making  one  circuit  through  the  constellations 
of  the  zodiac.  One  has,  therefore,  ample 
time  to  get  well  acquainted  with  him  before 
he  has  wandered  far  from  the  position  in 
which  one  first  found  him. 

For  nearly  six  months  each  year  Saturn 
shines  as  an  evening  star,  and,  returning  each 
207 


THE    WAYS    OF    THE    PLANETS 

year  as  he  does  with  such  slight  changes  of 
position,  he  comes  to  have  something  of  the 
stability  of  a  fixed  star.  Having  seen  him 
one  year,  we  can  count  on  his  returning  the 
next  only  about  thirteen  days  behind  time, 
and  but  little  farther  from  his  original  posi- 
tion than  twice  the  distance  between  the 
pointers  in  the  Big  Dipper. 

The  one  degree  a  month  which  he  travels 
along  the  ecliptic  is  toward  the  east,  except 
for  a  little  more  than  two  months  before 
opposition,  and  the  same  length  of  time 
afterward,  when  he  has  the  slight  apparent 
retrograde  motion  due  to  our  overtaking  and 
passing  him,  which  has  been  explained.  With 
Saturn  this  motion  is  so  slight — only  four 
degrees — that  it  does  not  put  him  much  out 
of  position,  and  it  is,  in  fact,  not  much  noticed 
except  by  close  observers.  He  has  all  the  time 
been  going  steadily  on  toward  the  east  (for 
the  retrograde  motion  is  only  an  apparent 
motion),  and  the  annual  change  of  twelve  de- 
grees in  position  is  always  in  this  direction. 

My  first  acquaintance  with  Saturn  was 
when  he  was  traveling  through  Pisces  and 
Aries,  where  there  are  no  first-magnitude 
stars  to  mark  the  path  of  the  wandering 
bodies  in  the  heavens.  It  was  then  that  I 
208 


SATURN 

was  most  impressed  with  the  fixity  and 
reliability  of  his  return.  Every  autumn  then 
for  five  years  we  watched  Antares  passing 
toward  the  west,  followed  by  the  little  "milk 
dipper"  in  Sagittarius;  and  then  Fomalhaut, 
crossing  the  sky  in  the  same  direction,  though 
below  the  constellations  of  the  zodiac;  and 
then  turned  our  eyes  toward  the  east,  know- 
ing that  the  next  bright  body  to  come  peep- 
ing over  the  tops  of  the  trees  would  be  Saturn. 
And  when  the  first  frosts  began  to  strip  the 
leaves  from  the  trees  we  found  the  com- 
pensation that  nature  always  gives  when  she 
destroys  one  beauty:  we  could  see  earlier 
in  the  evening,  through  the  bare  branches, 
that  lovely  yellowish  disc,  with  its  suggestion 
of  aloofness  and  grandeur  that  is  peculiar  to 
it.  For  the  face  of  Saturn,  while  never  what 
we  would  call  cold,  has  little  in  it  of  that 
bright,  warm,  friendly  aspect  which  is  at  times 
so  characteristic  of  Venus,  Mars,  and  Jupiter. 

AROUND     ONE     CIRCUIT    OF    THE    SKIES   WITH 
SATURN 

Saturn  is  now  (the  autumn  of  1912)  in  the 
first  part  of  his  path  through  Taurus,  and  he 
will  be  in  that  constellation  during  all  of 
1913  and  the  greater  part  of  1914. 
209 


THE    WAYS    OF    THE    PLANETS 

From  1912  to  1920  he  will  be  a  beautiful 
object  in  the  winter  sky,  threading  his  way 
slowly  through  that  splendid  galaxy  of  stars 
that  blazes  across  the  glittering  sky  peculiar 
to  the  cold  winter  nights.  He  will  pass  be- 
tween the  Pleiades  and  Aldebaran,  and  will 
be  in  opposition  in  that  region  on  November 
23,  1912.  Farther  east  in  the  constellation 
he  will  be  in  opposition  in  the  first  week  of 
December,  1913.  Almost  on  the  border  line 
between  Taurus  and  Gemini  he  will  be  in 
opposition  during  the  third  week  in  Decem- 
ber, 1914;  and,  as  this  is  very  near  the  peri- 
helion point  in  Saturn's  orbit,  the  planet  will 
then  be  at  his  brightest. 

In  1915  he  will  not  be  in  opposition  at  all; 
but  sometime  within  the  first  two  or  three 
days  of  1916  he  will  reach  that  position,  and 
will  then  be  well  on  in  his  journey  across 
Gemini.  For  these  four  years — from  1912 
to  1916 — he  will  be  visible  during  the  entire 
night,  at  the  times  of  his  opposition,  and  in 
his  best  condition.  The  rings  that  surround 
him  will  then  be  placed  so  that  we  will  get 
a  broad  expanse  of  light  from  them,  as  well 
as  from  the  planet  itself,  which  greatly  in- 
creases its  brightness. 

Saturn  will  then  continue  to  move  across 
210 


SATURN 

Gemini,  passing  in  the  early  part  of  1917 
under  Castor  and  Pollux,  and  very  near  to 
Neptune — a  meeting  which,  unfortunately, 
cannot  be  seen  with  the  naked  eye.  During 
this  year  (1917)  he  will  begin  his  journey 
through  the  smallest  of  all  the  constellations 
of  the  zodiac,  Cancer,  passing  near  the  lovely 
cluster  of  stars  we  call  the  Bee-hive,  and  will 
reach  Leo  early  in  1919,  where  he  will  remain 
until  about  the  end  of  1921.  While  in  this 
region  he  will  be  visible  during  the  winter 
and  all  of  the  spring  and  the  early  summer. 
All  three  of  these  constellations — Gemini, 
Cancer,  and  Leo — while  seen  in  the  winter, 
are  particularly  lovely  in  the  spring.  Gemini, 
in  the  beautiful  evenings  of  May,  hangs  with 
its  two  splendid  stars  in  the  northwest  above 
the  setting  sun;  and  with  the  soft  face  of 
Saturn  near  them,  these  stars  will  be  more 
than  ever  charming  in  the  two  seasons  that 
the  planet  remains  with  them. 

In  1917  Saturn  will  be  in  opposition  in  the 
region  of  Gemini,  about  the  middle  of  Jan- 
uary. In  1918  opposition  will  occur  about 
the  last  of  January,  and  Saturn  will  then  be 
in  Cancer.  The  next  year  he  will  be  in  op- 
position sometime  during  the  second  week 
in  February,  and  will  then  be  situated  be- 

15  211 


THE    WAYS    OF    THE    PLANETS 

tween  the  Bee-hive,  in  Cancer,  and  the  bril- 
liant first-magnitude  star  Regulus,  in  Leo. 
The  next  two  oppositions  will  be  in  Leo, 
about  thirteen  days  later  each  year.  Saturn 
will  then  pass  during  the  first  half  of  1922 
into  Virgo,  which  is  the  largest  of  all  the 
constellations,  and  he  will  remain  there  until 
three  oppositions  have  taken  place,  about 
thirteen  days  later  each  year. 

About  a  year  after  passing  Spica,  the  white, 
sparkling,  first-magnitude  star  in  Virgo, 
Saturn  will  enter  Libra,  crossing  that  con- 
stellation near  the  lower  part  of  the  square 
in  it.  From  there  he  will  go  through  Scorpio 
and  Sagittarius,  passing  above  Antares  and 
the  "milk  dipper,"  and  in  about  1932  will  have 
reached  that  comparatively  starless  region 
which  includes  a  part  of  Sagittarius  and  all 
of  Capricornus,  Aquarius,  Pisces,  and  Aries. 
For  the  next  nine  and  a  half  years  he  will 
give  distinction  to  this  part  of  the  heavens, 
and  thus  complete  his  circuit  of  twenty-nine 
and  a  half  years,  and,  with  never  resting, 
never  changing  movement,  will  start  on  a 
new  round,  with  a  new  generation  of  eyes 
following  his  fair  face  along  the  great  circle 
of  the  ecliptic. 

Saturn  is  brightest  when  he  is  in  Taurus,  not 

212 


SATURN 

far  from  Gemini,  as  he  will  be  in  1914,  and 
again  when  he  is  in  Scorpio,  as  he  will  be 
between  fourteen  and  fifteen  years  later.  The 
recurring  times  at  which  we  can  get  an  evening 
view  of  him  at  his  greatest  brightness  thus  al- 
ternate between  midwinter  and  midsummer. 
He  is  least  bright  when  he  is  in  the  last  half 
of  Leo  and  when  he  is  in  that  part  of  Aqua- 
rius above  Fomalhaut.  Between  these  posi- 
tions he  gradually  waxes  and  wanes  in  bright- 
ness, changes  that  are  largely  due  to  the 
position  of  his  rings. 

DISTANCE   AND   SIZE 

Saturn  is  almost  twice  as  far  from  the  sun 
as  Jupiter,  and  between  nine  and  ten  times 
farther  than  we  are.  His  mean  distance 
from  the  sun  is  eight  hundred  and  eighty- 
seven  million  miles;  but  his  distance  varies 
nearly  one  hundred  million  miles  between 
perihelion  and  aphelion.  His  orbit  is  only 
a  trifle  more  eccentric  than  that  of  Jupiter, 
but  the  variation  in  miles  is  so  much  greater 
because  the  orbit  is  so  much  larger. 

His  average  distance  from  the  earth  at 
opposition  is  seven  hundred  and  ninety-four 
million  miles,  but  at  the  most  favorable 
213 


THE    WAYS    OF    THE    PLANETS 

opposition  it  may  be  fifty  million  miles  nearer 
than  that.  At  conjunction  his  average  dis- 
tance is  nine  hundred  and  eighty  million 
miles;  but  his  greatest  possible  distance  at 
such  times  may  be  as  much  as  one  billion 
miles.  When  he  is  in  this  situation  it  takes 
light  a  little  more  than  an  hour  and  a  half 
to  pass  from  him  to  us.  At  his  nearest  we 
receive  light  from  him  in  about  an  hour  and 
six  minutes.  At  his  average  distance  from 
the  sun,  light  requires  about  an  hour  and 
twenty  minutes  to  go  from  one  to  the  other. 

While  Saturn  is  next  to  Jupiter  in  size  among 
the  planets,  he  is  not  as  large  as  Jupiter 
by  two- thirds,  but  his  mass  is  almost  three 
times  greater  than  that  of  all  the  other  plan- 
ets put  together  except  Jupiter.  It  is  ninety- 
five  times  greater  than  that  of  the  earth. 
In  diameter  Saturn  is  72,772  miles;  but  it 
is  more  flattened  at  the  poles  than  any  other 
planet,  and  in  consequence  there  is  a  differ- 
ence of  nearly  seven  thousand  miles  between 
its  polar  and  its  equatorial  diameters. 

The  density  of  Saturn  is  less  than  that  of 
any  other  planet,  and  it  is  ten  times  less 
than  that  of  the  earth.  No  other  planet  is 
less  dense  than  water;  but  Saturn  would 
float  in  water,  and  is  not  more  dense  than 
214 


SATURN 

cork.  On  account  of  its  mass  its  gravity  is 
greater  than  that  of  the  earth  by  about  one- 
tenth.  This  is  not  enough  to  make  a  very 
interesting  difference  in  the  weight  of  objects 
on  Saturn  and  on  the  earth.  The  average 
person  weighing  one  hundred  and  fifty  pounds 
here  would  weigh  only  one  hundred  and 
sixty-five  pounds  on  Saturn.  The  numer- 
ous penny-in-the-slot  weighing-machines  vary 
almost  that  much.  Saturn  has  eighty- three 
times  more  surface  than  the  earth,  and  more 
than  seven  hundred  and  fifty  times  the 
earth's  volume. 

SURFACE   ASPECTS   AND   CONSTITUTION 

It  is  not  at  all  certain  that  Saturn,  more  than 
Jupiter,  has  any  solid  surface.  Indeed,  it  is  al- 
most certain  that  it  has  not.  It  is  surrounded 
by  an  atmosphere  of  great  density,  and  we 
do  not  at  any  time  see  the  surface  of  the 
planet.  It  is  believed  probable  that  it  is 
at  least  largely  in  a  liquid  state,  if  not  to  a 
great  extent  even  gaseous. 

The  planet  is  certainly  not  in  any  way 

dependent  on  the  sun  for  the  extraordinary 

heat  that  everything  indicates  it  to  have, 

and  its  surface  is  brighter  than  it  is  believed 

215 


THE    WAYS    OF    THE    PLANETS 

it  could  be  if  shining  only  by  the  reflected 
light  of  the  sun.  This  does  not  mean  that 
Saturn  is  self-luminous;  but  it  is  nearly  cer- 
tain that  it  is  extremely  hot  and  glowing,  and 
its  brightness  may  be  in  part  due  to  its  own 
internal  fires  and  the  extremely  luminous 
and  dense  atmosphere  that  surrounds  it. 
It  receives  one  hundred  times  less  heat  and 
light  from  the  sun  than  we  do.  If  it  de- 
pended entirely  upon  the  sun  for  its  heat, 
the  temperature  would  be  nearly  three  hun- 
dred degrees  below  zero,  Fahrenheit.  It  is 
probably  not  only  very  hot  itself,  but  its 
heavy  atmospheric  envelope  perhaps  allows 
comparatively  little  heat  to  escape. 

Its  surface  is  belted  and  spotted  somewhat 
after  the  manner  of  Jupiter's,  but,  being  so 
much  farther  from  us  than  Jupiter,  it  does 
not  disclose  its  surface  features  with  the  same 
distinctness.  Apparently  it  is  much  less  tur- 
bulent than  Jupiter;  but  even  this  we  are 
not  quite  certain  of,  and  it  may  seem  more 
placid  because  we  do  not  so  well  see  its  agi- 
tations. 

Like  all  the  outer  planets,  it  differs  in  its 
constitution  from  the  earth  and  the  other 
inner  planets.  Its  atmosphere  contains  com- 
pounds with  which  we  are  not  familiar,  and 
216 


SATURN 

the  body  of  the  planet  itself  is  rarer  and 
lighter,  and  less  condensed,  and  in  a  much 
earlier  stage  of  evolution  than  the  earth  and 
the  small  planets  so  comparatively  near  us. 

DAY   AND   NIGHT 

The  length  of  Saturn's  day,  or  its  period 
of  rotation  on  its  axis,  is  about  ten  hours  and 
a  quarter.  Like  Jupiter,  it  has  slightly  dif- 
ferent rates  of  rotation  in  different  latitudes, 
thus  showing  its  lack  of  solidity.  The  rate 
of  rotation  has  been  determined,  as  in  the 
case  of  Jupiter,  by  observation  of  the  spots 
on  its  surface,  which,  while  they  are  not 
exactly  permanent,  yet  remain  apparently 
in  the  same  positions  for  months  and  even 
years  at  a  time,  and  are  thus  sufficiently 
stable  to  measure  a  rotation  of  so  short  a 
time  as  ten  hours. 

Whirling  over  at  this  rate  would  cause  the 
sun  to  appear  to  skim  across  the  sky  very 
swiftly  as  viewed  from  Saturn.  In  size,  it 
would  not  seem  more  than  three  times  as 
large  as  Venus  at  her  brightest  seems  to 
us,  and  every  minute  it  would  cover  a  dis- 
tance about  equal  to  the  diameter  of  the 
full  moon  as  we  see  it.  In  an  hour  it  would 
217 


THE    WAYS    OF    THE    PLANETS 

seem  to  move  more  than  six  times  as  far  as 
the  distance  between  the  " pointers."  At 
the  time  of  Saturn's  equinox  the  little  five- 
hour  day,  followed  by  the  equally  short  night, 
must  present  a  lively  aspect  with  the  sun 
racing  thus  swiftly  across  the  sky  in  daylight 
and  the  stars  sweeping  as  swiftly  over  at 
night.  If  things  remain  as  they  now  are, 
it  will  be  a  splendid  panorama  for  the  people 
there  when,  in  the  far-distant  future,  Saturn 
may  have  cooled  and  solidified  sufficiently 
to  maintain  life  somewhat  as  we  know  it. 
The  earth,  though,  and  Venus  and  Mars 
would  be  from  Saturn  only  telescopic  objects 
to  eyes  like  ours,  and  Jupiter  no  brighter 
than  he  is  to  us.  Thus  does  our  brother  Sat- 
urn pay  the  price  of  his  remoteness  from  the 
rest  of  the  solar  family. 

THE   RINGS   AND   MOONS   OF   SATURN 

But  the  circling  stars  and  the  swift-moving 
sun  are  the  least  part  of  the  splendid  spec- 
tacle that  might  be  seen  from  Saturn.  He 
is  surrounded  with  no  less  than  ten  moons 
of  more  or  less  imposing  size,  and  in  addition 
has  three  rings  circling  around  with  him, 
composed  of  myriads  of  small  satellites,  to- 
218 


SATURN 

gether  forming  a  band  the  outer  diameter 
of  which  is  something  more  than  twenty- 
one  times  broader  than  the  diameter  of  the 
earth.  These  are  the  famous  rings  of  Saturn, 
the  only  objects  of  their  kind  in  the  solar 
system,  intensely  interesting  to  scientific  ob- 
servers, wonderful  to  the  curious,  and  splen- 
didly beautiful  to  everybody.  It  is  this  pro- 
fusion of  rings  and  moons  that  entitles 
Saturn  to  be  called,  as  he  often  has  been, 
the  most  spectacular  of  all  the  planets. 

The  outer  ring  is  nearly  ten  thousand 
miles  broad,  and  is  separated  from  the  next 
one  by  a  space  of  about  seventeen  hundred 
miles.  The  second  ring  is  nearly  eighteen 
thousand  miles  across.  It  is  very  bright  on 
the  outer  edge,  but  gradually  grows  less  so, 
until,  with  a  not  very  perceptible  division,  it 
fades  into  the  inner  ring,  which  is  but  slightly 
luminous,  and  is  called  the  crape  ring.  This 
is  about  nine  thousand  miles  broad  and  nearly 
ten  thousand  miles  from  Saturn.  This  gradual 
fading  of  the  rings  to  a  dusky  hue  toward 
the  center,  and  then  the  blackness  of  the 
space  between  them  and  the  planet,  gives 
them  from  certain  points  of  view  a  nest- 
like  appearance;  and  my  first  impression  of 
Saturn,  when  I  saw  him  through  the  tele- 
219 


THE    WAYS    OF    THE    PLANETS 

scope,  was  that  he  was  nestling  in  a  concave 
body  of  light — an  appearance  that  is  in- 
tensified by  his  extreme  flatness  at  the  poles. 

Notwithstanding  the  imposing  breadth  of 
these  rings,  they  are  less  than  a  hundred 
miles  in  thickness.  They  are,  in  fact,  noth- 
ing more  than  an  untold  number  of  tiny 
satellites  revolving  about  Saturn  in  the  same 
plane  and  close  enough  together  to  appear, 
at  the  distance  they  are  from  us,  as  if  they 
were  one  body.  Just  how  close  they  are 
together,  and  how  they  appear  when  near 
by,  we  do  not  yet  know.  It  was  first  shown 
by  mechanical  laws  that  they  must  be  com- 
posed of  separate  bodies;  the  spectroscope 
shows  that  they  are;  and  it  has  recently  been 
thought  that  they  have  even  been  seen  to  be 
so  through  a  telescope. 

Being  all  in  the  same  plane,  they  form  a 
flat,  broad,  thin  ring,  so  thin  that  when  the 
edge  of  the  ring  is  turned  toward  us  we  can- 
not see  them  at  all.  We  never  see  them  at 
their  full  breadth.  If  we  did,  Saturn  would 
be  much  brighter  at  times  than  he  ever  is. 
The  plane  in  which  they  revolve  is  the  plane 
of  Saturn's  equator;  and  the  axis  of  Saturn, 
with  the  rings,  has  a  tilt  of  twenty-seven 
degrees  in  his  orbit.  The  result  of  this  is 
220 


"  3 

•n     O 
£    c« 


SATURN 

that  at  the  time  of  Saturn's  equinoxes  the 
edge  of  the  rings  is  turned  toward  us,  and 
they  practically  disappear.  Half-way  be- 
tween the  equinoxes  they  are  open  again  as 
far  as  they  ever  are  to  our  view.  This  is 
why  Saturn  alternates  in  brightness.  The 
times  of  his  equinoxes  occur  every  fourteen 
and  eight- tenths  years,  and  he  is  then  alter- 
nately in  Leo  and  Aquarius  and  is  least 
bright.  The  times  at  which  the  rings  are 
most  open  occur  at  intervals  of  the  same 
length,  and  he  is  then  alternately  in  Scorpio 
and  Taurus  and  at  his  brightest. 

It  is  believed  that  Saturn's  rings  were 
never  a  part  of  the  planet,  but  are  mere 
particles  of  cosmic  materials  which  happened 
to  be  left  over,  and  which  he  has  gathered 
up  by  his  force  of  gravity  and  compelled  to 
revolve  about  him. 

Saturn,  more  fortunate  than  Jupiter,  has 
escaped  the  unimaginative  naming  of  his 
moons  by  number,  though  one  would  think 
that,  having  such  a  numerous  offspring,  a 
shortage  in  names  would  be  more  likely  to 
occur  in  his  than  in  any  other  planet  family. 
They  all  have  names  more  or  less  connected 
with  the  great  god  whose  name  the  planet 
bears,  and  are,  in  order  of  their  distance 

221 


THE    WAYS    OF    THE    PLANETS 

from  Saturn:  Mimas,  Enceladus,  Tethys, 
Dione,  Rhea,  Titan,  Hyperion,  Japetus, 
Phoebe,  and  Themis.  The  largest  and 
brightest  of  them  all  is  Titan.  It  is  larger 
than  our  moon,  which  is  one  of  the  large 
moons  in  the  solar  system,  or  than  Mercury, 
and  is  not  much  smaller  than  Mars.  It  is 
more  than  three-quarters  as  large  as  all  the 
other  moons  of  Saturn  put  together.  Natu- 
rally, it  was  the  first  to  be  discovered,  and 
was  under  observation  as  long  ago  as  1655. 
Rhea  and  Japetus  are  next  in  size,  and  were 
discovered  in  1671-72;  Dione  and  Tethys 
were  both  discovered  in  1684,  and  Enceladus 
and  Mimas  in  1789. 

Until  1848  seven  moons  were  all  that  were 
known  to  belong  to  Saturn.  In  that  year 
little  Hyperion,  whose  diameter,  it  is  thought, 
can  hardly  exceed  two  hundred  miles,  came 
into  our  view.  A  little  more  than  fifty  years 
later  (in  1898)  Phoebe  made  her  bright  mark 
on  a  photographic  plate  at  Harvard,  and 
was  caught.  By  tracing  her  from  one  plate 
to  another  her  orbit  was  computed,  her 
probable  size  determined,  and  practically  all 
that  is  known  about  her  was  found  out  be- 
fore she  was  seen,  which  was  not  until  1904. 
She  is  not  much  larger  than  a  good-sized 

222 


SATURN 

mountain,  but  is  a  unique  and  interesting 
little  satellite  that,  far  outside  of  the  paths 
of  any  of  the  other  moons,  circles  in  an  ec- 
centric orbit  around  Saturn  in  an  opposite 
direction  from  the  rest  of  the  satellites,  and 
thus  gives  rise  to  many  interesting  astro- 
nomical speculations.  Themis,  also  a  tiny 
body,  was  discovered  in  the  same  way  in 
1906,  and  is  thought  to  be  the  smallest  body 
in  the  solar  system.  Titan  is  the  only  one 
of  this  group  of  satellites  whose  true  disc 
we  can  see  even  with  a  telescope.  Only  one 
other  (Rhea)  can  be  seen  in  transit  across 
the  planet.  The  others  are  not  much  more 
than  bright  points  of  light,  while  Phcebe  and 
Themis  are  almost  at  the  limit  of  visibil- 
ity. 

On  account  of  their  great  distance  from 
the  sun  Saturn 's  moons  are,  of  course,  not 
very  bright,  and  all  of  them  put  together  do 
not  give  one-tenth  as  much  light  to  Saturn 
as  we  receive  from  our  moon.  But,  such  as 
they  are,  they  may  some  day  be  very  useful 
to  Saturn  as  a  means  of  illumination.  Re- 
ceiving as  he  does  a  hundred  times  less  light 
from  the  sun  than  we  do,  he  may  be  some 
day  much  in  need  of  the  light  reflected  from 
all  his  rings  and  moons. 
223 


THE    WAYS    OF    THE    PLANETS 

SEASONS 

The  seasons  on  Saturn  are  somewhat  like 
ours  in  the  succession  of  spring,  summer, 
autumn,  and  winter;  but  the  inclination  of 
its  axis  to  its  orbit  being  twenty-seven  de- 
grees instead  of  twenty-three  and  a  half,  as 
ours  is,  each  season  is  much  more  accentu- 
ated than  ours.  The  sun  climbs  higher  dur- 
ing the  northern  summer,  and  sinks  corre- 
spondingly lower  during  the  winter.  But  in 
length  Saturn's  seasons  are  very  different 
from  ours.  Like  his  year,  they  are  about 
twenty-nine  and  one-half  times  as  long  as 
ours.  Each  one  is  more  than  seven  years 
long.  Even  the  agreeable  seasons  might 
grow  monotonous  to  one  in  that  time;  but 
to  be  spinning  through  the  rapidly  alternat- 
ing days  and  nights  of  Saturn  during  seven 
long  years  of  winter  is  a  situation  that  one 
does  not  care  to  contemplate.  It  is  with 
world  personalities  as  with  human  per- 
sonalities: however  much  we  may  admire 
their  superior  grandeur,  when  we  consider 
details  we  would  not  change  places  with  them. 

The  symbol  of  Saturn  is  an  ancient  scythe 
(^),  which  gets  its  appropriateness  from 
the  fact  that  the  deity  of  that  name  was  the 
special  protector  of  agriculture. 


XV 

URANUS 

VENUS,  Mars,  Jupiter,  and  Saturn,  bril- 
liant beauties  that  they  are,  have  al- 
ways been  distinguished  features  of  the 
heavenly  view.  The  records  of  Mercury  do 
not  go  back  so  far  as  those  of  these  more 
easily  seen  planets,  yet  there  is  no  reason 
to  think  that  he  has  not  been  always  known, 
though  less  widely,  perhaps,  than  the  four 
planets  more  frequently  in  view.  To  Uranus 
belongs  the  distinction  of  being  the  first 
planet  that  was  discovered — a  distinction 
that  one  cannot  help  but  feel  was  too  long 
delayed,  for  it  did  not  come  until  1781.  For 
ages  and  ages  his  lovely  pale  beams  had  been 
shining  down  upon  us  from  his  little  disc, 
no  fainter  in  brilliancy  than  many  a  sixth- 
magnitude  star  (a  degree  of  brightness  which 
we  think  is  within  the  limit  of  good  vision, 
even  in  these  days),  and  no  human  being  had 
been  conscious  that  this  bright  body  was 
225 


THE    WAYS    OF    THE    PLANETS 

only  another  member  of  the  solar  family, 
circling  with  the  rest  of  us  around  our  parent, 
the  sun,  and  having  nothing  in  common  with 
the  far-off  stars  among  which  we  had  num- 
bered him.  Nineteen  times  he  had  been 
charted  as  a  fixed  star  before  his  identity 
was  suspected,  and  after  he  became  known 
to  us  as  a  planet  he  was,  by  means  of  these 
charts,  traced  back  for  one  hundred  and 
thirty  years,  and  much  information  was 
thus  gained  concerning  his  orbit  and  move- 
ments. 

Uranus  was  not,  however,  discovered 
through  observation  of  his  movement  among 
the  stars.  A  view  of  his  actual  disc  was 
caught  by  the  musician  and  astronomer, 
Herschel,  as  he  gleaned  with  his  telescope 
in  that  part  of  the  sky  where  the  planet 
lay,  one  hundred  and  seventy-one  years  after 
the  invention  of  that  aid  to  vision.  It  was 
at  first  thought  that  a  comet  had  been  dis- 
covered, but  later  investigation  showed  a 
much  more  important  member  of  the  solar 
system,  and  the  discovery  of  a  new  planet 
was  announced. 

George  III.  was  then  King  of  England, 
and  the  loyal  Herschel  called  the  planet 
Georgium  Sidus  in  honor  of  that  monarch. 
226 


URANUS 

Fortunately,  the  world-wide  interest  in  this 
newly  discovered  body  saved  it  from  so 
local  an  appellation,  and  it  finally  came  to  be 
called  after  Uranus,  the  father  of  Saturn,  a 
name  somewhat  more  in  keeping  with  its 
place  among  the  planets.  In  England,  how- 
ever, a  very  commendable  loyalty  to  Her- 
schel  has  resulted  in  the  planet's  sometimes 
being  called  Herschel,  after  its  discoverer, 
and  we  see  this  name  often  in  English  books 
on  astronomy,  especially  the  older  books; 
but  Uranus  is  now  the  generally  accepted 
name. 

The  symbol  of  the  planet  as  it  appears  in 
all  almanacs — at  least  in  all  English  almanacs 
— is  a  capital  H  with  a  planet  swinging  from 
the  cross-bar  in  the  letter,  thus  3£ .  And  to 
this  extent  the  discovery  of  the  planet  by 
Herschel  is  commemorated.  In  American 
almanacs  the  symbol  is  contracted  into  this 
figure  $. 

It  is  a  matter  for  regret  that  Uranus  does 
not  come  more  easily  within  our  view;  for 
he  is  a  very  beautiful  planet,  pale  green  in 
color,  and  unlike  any  of  the  others  in  his 
aspect.  There  are,  however,  very  few  per- 
sons nowadays  who  can  see  him  without  the 
aid  of  at  least  a  small  glass,  and  to  most  of 

16  227 


THE    WAYS    OF    THE    PLANETS 

us  he  must  ever  remain  a  body  with  which 
we  can  have  no  personal  acquaintance. 
None  the  less  he  must  have  an  interest  to 
us  such  as  attaches  always  to  anything  so 
closely  related  to  us,  and  sharing  with  us  a 
common  origin  and  a  common  destiny.  To 
those  who  have  unusually  keen  vision — or  a 
small  telescope — there  will  be  much  pleasure 
in  viewing  the  planet.  But  even  to  those 
who  have  not  these  facilities  for  seeing,  it 
ought  to  be  interesting  to  know  in  what 
region  of  the  skies  this  far-off  member  of 
our  family  dwells,  what  his  wanderings  are, 
and  something  of  his  personality  and  habits. 

It  requires  a  few  days  more  than  eighty- 
four  years  for  Uranus  to  make  one  revolution 
around  the  sun,  so  that  he  moves  even  more 
slowly  than  Saturn  from  one  constellation 
to  another;  and  if  we  could  only  see  him 
more  easily,  he  would  be  scarcely  more  diffi- 
cult to  keep  track  of  than  a  fixed  star.  He 
remains  in  each  constellation  somewhere 
near  seven  years  and  his  change  of  place 
in  the  skies  amounts  in  one  year  to  but  little 
more  than  four  degrees,  which  is  less  than 
the  distance  between  the  pointers. 

Since  Uranus  was  discovered  he  has  made 
one  circuit  of  the  skies,  which  he  finished  in 
228 


URANUS 

1865,  and  he  is  now  (1912)  more  than  half- 
way around  on  another.  His  position  now 
is  in  Capricornus,  nearly  twenty  degrees  east 
of  the  "milk  dipper"  in  Sagittarius,  and  for 
the  next  quarter  of  a  century  he  can  be  seen 
by  any  who  have  eyes,  or  a  glass,  to  accom- 
plish this  during  the  summer  evenings.  Each 
year  he  will  be  about  seven  degrees  farther 
east.  He  is,  however,  still  pretty  far  south 
of  the  equator,  and  not  so  easily  seen  as  he 
will  be  when  he  reaches  that  part  of  the 
ecliptic  which  runs  somewhat  higher  in  the 
skies.  Even  an  opera-glass  will  bring  Uranus 
into  the  view  of  many  persons.  His  path 
deviates  very  little  from  the  line  of  the 
ecliptic — never  quite  so  much  as  half  a  de- 
gree. The  knowledge  of  this  makes  it  less 
difficult  to  find  him.  ,; 

The  synodic  period  of  Uranus  is  about 
three  hundred  and  sixty-nine  days,  so  that 
an  opposition  occurs  about  four  or  five  days 
later  each  year.  He  was  in  opposition  this 
year  (1912)  on  July  24th.  In  1913  an  opposi- 
tion will  take  place  on  July  29th,  and  in  1914 
on  August  2d,  and  oppositions  will  occur 
about  four  days  later  each  year  thereaf- 
ter. 

Uranus  is  twice  as  far  from  the  sun  as 
229 


THE    WAYS    OF    THE    PLANETS 

Saturn  is,  and  nineteen  times  as  far  as  the 
earth.  Its  mean  distance  from  the  sun  is 
1,784,732,000  miles,  and  at  this  distance 
more  than  two  hours  and  a  half  would  be 
required  for  light  to  travel  from  the  sun  to 
the  planet.  Viewed  from  the  planet,  the 
sun  would  appear  only  about  two  and  a  half 
times  larger  than  Jupiter  appears  to  us,  and 
the  earth  would  be  a  very  small  telescopic 
body,  if,  indeed,  it  would  be  visible  at  all. 
Even  at  this  great  distance  from  the  sun,  and 
with  the  sun  showing  so  small  as  it  does,  the 
planet  would  still  have  more  than  a  thousand 
times  as  much  light  as  we  get  from  our  moon, 
and  so  in  this  respect  might  be  fairly  com- 
fortably provided  for  even  for  eyes  con- 
structed like  those  of  human  beings.  The 
heat  the  sun's  radiant  energy  furnishes  to 
Uranus  is,  from  our  point  of  view,  almost  a 
negligible  quantity.  If  there  were  no  other 
source  of  supply,  the  normal  temperature  of 
the  planet  would  be  more  than  three  hundred 
degrees  below  zero,  Fahrenheit.  There  is  no 
reason  to  think,  however,  that  this  is  the  tem- 
perature that  prevails  on  Uranus.  As  far 
as  we  can  tell,  it  has  a  dense  and  extensive 
atmosphere,  and  probably  very  considerable 
internal  heat. 

230 


URANUS 

Uranus  is  smaller  than  either  Jupiter  or 
Saturn;  but  it  is  much  larger  than  Mars, 
Venus,  Mercury  and  the  earth  combined. 
Its  diameter  is  nearly  thirty-three  thousand 
miles.  Its  volume  is  sixty-five  times  as 
great  as  that  of  the  earth;  but  its  mass  is 
only  about  fourteen  times  the  mass  of  the 
earth,  which  shows  it  to  be  a  very  much 
expanded  body.  It  is  slightly  more  dense 
than  water,  but  only  about  two-tenths  as 
dense  as  the  earth.  Its  force  of  gravity  is 
small  for  so  large  a  body — only  about  nine- 
tenths  that  of  the  earth. 

There  is  every  indication  that  the  planet 
is  not  a  solid  body  at  all,  and  that  it  is,  per- 
haps, largely  vapor.  We  undoubtedly  can- 
not see  the  surface  of  it;  but  through  the 
telescope  it  faintly  shows  the  same  belted 
appearance  that  we  see  on  Jupiter  and 
on  Saturn,  though  it  is  difficult  to  see  the 
belted  region,  which  is  near  the  equator,  be- 
cause the  axis  of  the  planet  is  so  inclined  to 
its  orbit  that  much  of  the  time  the  poles  are 
pointed  almost  toward  us.  The  spectroscope 
indicates  something  of  the  same  materials  in 
its  atmosphere  that  the  other  large  and  far- 
away planets  have,  and  there  is  no  reason  to 
doubt  that  the  planet  is  in  a  much  earlier 
231 


THE    WAYS    OF    THE    PLANETS 

stage  of  development  than  any  of  the  terres- 
trial planets. 

We  really  know  nothing  certainly  about 
the  rotation  of  Uranus;  but  there  seems  to 
be  some  indication  that,  like  Jupiter  and 
Saturn,  it  revolves  swiftly — in  perhaps  ten 
or  twelve  hours,  and  hence  has  a  very  short 
day  and  night.  The  great  inclination  of 
its  axis  must  make  its  seasons  so  abnormal, 
from  our  point  of  view,  that  it  is  difficult  to 
understand  what  they  are.  Moreover,  the 
planet  is,  at  this  stage  of  its  development, 
so  far  from  being  a  habitable  body,  for 
beings  such  as  we  know  anything  about, 
that  the  subject  of  its  seasons  seems  not 
very  important  or  interesting. 

It  seems  but  fitting  that  this  vapory,  pale 
green  planet  should  have  satellites  with  the 
fairy  names  of  Ariel,  Umbriel,  Titania,  and 
Oberon.  One  can  forgive  a  good  many 
utilitarian  feats  in  nomenclature  for  the  sake 
of  these  charmingly  appropriate  names  for 
the  satellites  of  Uranus.  Titania  and  Oberon 
were  discovered  in  1787  by  Herschel,  the 
discoverer  of  the  planet.  They  are  not  very 
much  farther  from  Uranus  than  our  moon 
is  from  us,  and  are  easily  seen  with  a  tele- 
scope. Titania,  the  nearer  to  Uranus  and 
232 


URANUS 

the  larger,  is  probably  about  one  thousand 
miles  in  diameter;  and  Oberon  is  not  very 
much  smaller.  In  1852  Umbriel  and  Ariel 
were  discovered.  They  are  both  smaller  and 
nearer  to  Uranus  than  either  of  the  two  first 
discovered,  and  are  seen  with  considerable 
difficulty,  because  of  their  proximity  to  the 
larger  and  brighter  body  of  the  planet. 
There  is  not,  however,  very  much  difference 
between  any  of  the  four  in  real  brightness. 


XVI 

NEPTUNE 

IT  is  rather  curious  to  what  extent  we  have 
a  feeling  of  kinship  with  Neptune,  not- 
withstanding he  dwells  forever  in  far-off 
space  where  we  cannot  expect  even  to  have 
a  glimpse  of  him  without  the  aid  of  a  tele- 
scope. Uranus,  the  other  very  distant  planet, 
is  so  nearly  within  the  limit  of  ordinary 
vision  that  we  have  always  a  hope  that,  by 
some  lucky  chance  of  situation  or  atmos- 
phere, we  may  some  day  be  able  to  see  him 
face  to  face,  and  know  for  ourselves  what 
manner  of  planet  this  is  which,  though  a 
member  of  our  own  cosmic  family,  remains 
always  just  beyond  easy  exchange  of  glances 
with  us ;  and  so  we  in  a  measure  keep  a  look- 
out for  him  that  gives  us  a  sense  of  his  reality. 
With  Neptune  there  can  be  no  feeling  of 
this  sort  to  keep  us  with  a  lively  interest  in 
him,  and  yet  he  is  hardly  less  real  to  us  than 
Uranus,  and  we  have  a  more  intimate  sense 
234 


NEPTUNE 

of  nearness  to  him  than  we  have  for  any 
fixed  star.  Far  away  as  he  is,  the  distance 
between  us  is  short  compared  with  the  many 
trillions  of  miles  farther  that  we  must  go 
to  reach  the  nearest  star,  and  in  thinking 
of  him  we  always  have  a  sense  of  this.  Then, 
however  aloof  he  may  keep  himself  from  this 
cozy  little  bunch  of  planets  near  the  sun,  of 
which  the  earth  is  one,  he  is  still  of  the  same 
parentage  with  us,  and  his  life  history  is 
part  of  our  family  history,  so  that  we  can 
never  feel  indifferent  to  what  concerns  him. 

Close  as  Neptune  is  to  us  in  kinship  and 
distance,  as  astronomical  distances  go,  we 
never  knew  of  his  existence  until  sixty-six 
years  ago.  He  is  to  us  almost  a  recent 
arrival  in  the  solar  domain,  but  we  know 
that  he  has  been  here  as  long  as  we  have; 
and  whether  he  was  detached  before  we  were 
from  the  great  nebula  which  gave  birth  to 
us  all,  or  at  about  the  same  time,  we  know 
that  for  long  ages  before  there  were  eyes 
on  the  earth  to  see  him  he  was,  as  he  still 
is,  circling  slowly  and  majestically  around 
our  common  center  of  control. 

The  discovery  of  Neptune  in  1846  created 
truly  a  sensation  in  astronomical  circles. 
And,  unlike  most  sensational  happenings,  it 
235 


THE    WAYS    OF    THE    PLANETS 

fully  justified  the  extreme  interest  it  aroused. 
The  computation  that  led  to  it  was  a  mathe- 
matical triumph,  and  the  final  result  was  a 
most  splendidly  convincing  proof  of  the 
theory  of  gravitation.  For  the  place  of  this 
hitherto  unknown  planet  was  found  by 
means  of  computations  based  on  the  fact 
that  at  certain  times  Uranus  went  a  little 
out  of  his  way,  thus  showing  some  disturb- 
ing body  outside  of  his  orbit  pulling  him 
slightly  from  the  course  he  would  otherwise 
take.  The  deviation  was  not  much — only 
about  one  and  three-fourths  of  a  minute, 
which  is  equal  to  about  one-seventeenth  of 
the  apparent  diameter  of  the  moon,  or  one- 
sixth  of  the  distance  between  Mizar  and 
Alcor,  situated  at  the  bend  of  the  handle  of 
the  Big  Dipper,  two  stars  that  it  is  difficult 
for  some  eyes  to  separate.1  But  this  slight 
irregularity  of  Uranus  was  enough  to  set  at 
least  two  able  men  at  work  in  an  effort  to 
locate  the  disturbing  cause.  These  two  men 
were  Adams,  of  England,  and  Leverrier,  of 
France. 

The  result  of  Adams's  work  was  announced 
to  the  Astronomer  Royal  in  England  in  the 

^ee,  in  The  Friendly  Stars,  "The  Seven  Stars  of  the 
Dipper." 

236 


NEPTUNE 

autumn  of  1845;  but  the  actual  search  for 
the  planet  in  the  place  predicted  was  delayed 
until  the  following  summer.  In  the  mean 
time  Leverrier  had  completed  his  work  and 
had  communicated  with  astronomers  in  Ber- 
lin, directing  them  where  to  look  for  the 
planet.  The  facilities  for  that  sort  of  work 
were  then  better  in  Berlin  than  in  England; 
and  within  half  an  hour  after  the  search 
was  begun,  on  the  night  of  September  23, 
1846,  the  new  planet  was  discovered  a  little 
more  than  half  a  degree  from  the  exact 
position  Leverrier  had  found  for  it.  It  was 
first  recognized  as  having  a  sensible  disc, 
and  within  a  day  its  motion  was  apparent. 
No  wonder  the  astronomical  world  was 
thrilled  by  this  achievement! 

Although  the  planet  was  actually  dis- 
covered by  following  the  directions  of  Lever- 
rier, it  was  found  that  it  might  have  been 
seen  months  before  if  the  English  astron- 
omers had  shown  more  promptness  in  using 
the  computations  of  Adams;  and  there  has 
always  been  a  disposition  among  astrono- 
mers, both  in  France  and  in  England,  to  give 
both  men  credit  for  their  extraordinary 
achievement,  though,  naturally,  there  is 
somewhat  more  stress  laid  upon  the  work  of 
237 


THE    WAYS    OF    THE    PLANETS 

each  in  his  own  country.  The  newly  dis- 
covered body  was  at  first  named  for  its  dis- 
coverer, Leverrier,  but  a  sense  of  justice 
to  Adams  prevailed  to  such  an  extent  that 
in  the  end  a  less  commemorative  name  was 
chosen,  and  the  planet  was  called  after 
Neptune,  the  son  of  Saturn  and  the  brother 
of  Jupiter — a  name  more  fitting,  on  the  whole, 
for  a  member  of  this  planet  family,  whose 
other  members  all  bear  the  names  of  some  of 
the  ancient  deities.  The  trident  (f  ),  Nep- 
tune's three-pronged  spear,  is  the  symbol 
of  the  planet. 

The  mean  distance  of  Neptune  from  the 
sun  is  more  than  two  and  a  half  billion  miles 
(2,790,000,000),  and  his  orbit  is  so  nearly 
circular  that  the  variation  between  his  peri- 
helion and  aphelion  distance  is  only  about 
fifty  million  miles.  His  orbit  is,  in  fact,  less 
eccentric  than  that  of  any  other  planet  ex- 
cept Venus.  His  immense  distance  from  the 
sun,  of  course,  deprives  him  of  any  great 
amount  of  heat  or  light  from  that  source 
as  compared  with  the  other  planets.  The 
sun  would  appear  to  an  observer  on  Neptune 
a  little  smaller  than  Venus  appears  to  us. 
But  so  great  is  the  intensity  of  its  radi- 
ance that  even  as  so  diminutive  a  sun  as 
238 


NEPTUNE 

that  it  would  give  to  Neptune  more  than 
six  hundred  times  as  much  light  as  our  full 
moon  gives  to  us.  This,  however,  would 
be  as  much  as  nine  hundred  times  less  light 
than  we  get  from  the  sun.  Such  light  as  the 
planet  receives  from  the  sun  reaches  it  after 
a  journey  of  a  little  more  than  four  hours. 

Of  the  heat  the  planet  has,  either  inherent 
or  acquired  from  the  sun,  we  do  not  know 
much.  The  normal  temperature  at  that 
distance  from  the  sun  would  be  more  than 
three  hundred  and  sixty  degrees  below  zero, 
Fahrenheit,  and  there  is  not  much  to  indi- 
cate in  what  state  the  planet  is  with  refer- 
ence to  its  own  heat.  Investigations  thus 
far  made  do  not  show  it  to  be  so  intensely 
hot  as  Jupiter  and  Saturn  undoubtedly  are; 
but  with  its  heavily  vapor-laden  atmosphere 
it  could  not  have  the  frigidity  normal  to  a 
black,  unprotected  body  at  its  distance  from 
the  sun. 

Neptune  is  thought  to  have  an  immense 
atmosphere,  and,  like  the  other  outer  planets, 
one  of  a  composition  not  wholly  familiar  to 
us.  Consequently  we  do  not  know  as  yet 
just  what  this  atmosphere  does  for  the 
planet.  It  has  a  fairly  good  reflecting  pow- 
er, though  the  planet,  on  the  whole,  is  darker 
239 


THE    WAYS    OF    THE    PLANETS 

in  color  than  Jupiter  or  Saturn.  Its  color 
is  of  that  bluish  cast  which  sometimes  sug- 
gests a  leaden  appearance.  The  color,  as 
well  as  the  fact  that  Neptune  is  denser  than 
any  of  the  other  outer  planets,  indicates  that 
it  may  be  in  a  more  advanced  stage  of  de- 
velopment than  at  least  Jupiter  and  Saturn 
are,  and  perhaps  than  Uranus  is. 

That  Neptune  has  made  greater  progress 
toward  solidity  (though  it  is  still  very  far 
from  that  state)  than  the  other  outer  planets 
is  suggested  also  by  its  size;  for,  as  we  have 
seen,  the  smaller  planets  develop  more  rap- 
idly than  the  larger  ones.  The  diameter  of 
Neptune  is  a  little  less  than  thirty  thousand 
(29,827)  miles.  The  planet  is  somewhat 
smaller,  therefore,  than  Uranus,  and  much 
smaller  than  Jupiter  or  Saturn.  But  as 
compared  with  the  earth,  the  largest  of  the 
inner  planets,  it  is  a  vastly  greater  body. 
Its  mass  is  seventeen  times  more  than  that 
of  the  earth;  its  surface  is  as  much  as  six- 
teen times  more  extensive  than  the  earth's; 
and  its  volume  is  more  than  eighty  times 
greater  than  the  volume  of  the  earth. 

Of  the  time  of  Neptune's  rotation  on  its 
axis  very  little  is  known.  That  little,  how- 
ever, indicates  a  slower  rotation  than  the 
240 


NEPTUNE 

other  planets  seem  to  have,  and  the  alterna- 
tions of  day  and  night  on  Neptune  are,  there- 
fore, probably  less  swift  than  on  Jupiter  and 
on  Saturn.  The  planet  is  too  far  away  for 
us  to  see  its  surface  markings  with  any  dis- 
tinctness, but  there  are  indirect  processes 
by  which  we  can  get  approximate  informa- 
tion concerning  the  facts  about  rotation. 
One  of  these  processes  is  by  observation  of 
the  motions  of  the  satellites.  Of  these  use- 
ful bodies  Neptune,  fortunately,  has  one — 
a  very  excellent  moon  about  the  size  of  our 
own.  It  has  some  eccentricities,  such  as 
revolving  about  the  planet  in  the  opposite 
direction  from  that  which  the  more  conven- 
tional satellites  follow,  and  having  an  orbit 
a  good  deal  inclined  to  the  plane  of  the 
equator  of  the  parent  body.  But  it  is  a  very 
interesting  moon  to  astronomers,  and  will 
no  doubt  in  time  help  to  make  clear  some 
things  in  the  history  of  Neptune  which  are 
now  not  quite  understood. 

Being  so  far  from  the  sun,  Neptune  moves, 
of  course,  very  slowly  in  comparison  with 
the  nearer  planets,  though  his  speed  is  at 
the  rate  of  three  and  a  half  miles  a  second, 
which,  after  all,  does  not  denote  any  high 
degree  of  sluggishness.  His  change  of  posi- 


THE    WAYS    OF    THE    PLANETS 

tion  in  the  sky  amounts  to  a  little  more  than 
two  degrees  a  year;  so  that  in  an  ordinary 
lifetime  he  does  not  make  any  very  great 
progress  along  the  zodiac. 

When  Neptune  was  discovered  he  had  just 
left  the  constellation  Capricornus,  and  in  the 
sixty-six  years  that  his  movements  have  been 
followed  he  has  passed  through  Aquarius, 
Pisces,  Aries,  Taurus,  and  is  now  (1912)  in 
Gemini,  very  near  Castor  and  Pollux.  The 
time  required  for  his  circuit  around  the  sun 
is  nearly  one  hundred  and  sixty-five  (164.6) 
years,  so  that  he  remains  for  about  thir- 
teen years  in  each  constellation.  He  will 
complete  one  sidereal  period,  dating  from 
the  time  of  his  discovery,  in  the  year 
2011. 

The  apparent  motion  of  Neptune  is  direct 
a  little  more  than  six  months  in  the  year,  and 
retrograde  a  little  more  than  five  months,  so 
that  it  seems  to  present  the  old  mental  arith- 
metic problem  of  the  climber  that  fell  back 
so  much  every  time  after  he  had  climbed 
a  certain  number  of  feet.  But  the  falling 
back  in  the  case  of  Neptune  is  an  illusion, 
as  we  know.  He  keeps  straight  on  in  his 
journey,  as  we  may  see  if  we  watch  him 
from  year  to  year,  and  his  change  of  position 
242 


NEPTUNE 

is  so  slight  during  any  year  that  the  change 
of  direction  is  hardly  noticeable. 

Neptune  is  as  bright  as  an  eighth-magni- 
tude star,  and  it  is  possible  to  see  him  with 
a  good  field-glass.  The  difficulty  is  in  dis- 
tinguishing him  from  a  star,  for  his  disc  does 
not  show  except  through  a  telescope.  If  one 
has  such  a  glass,  however,  it  will  be  worth 
while  to  direct  it  toward  that  part  of  the 
ecliptic  just  under  Castor  and  Pollux  any 
time  within  the  next  two  or  three  years,  and 
a  sight  of  this  yet  strange  brother  planet 
may  be  the  reward.  He  will  be  in  opposi- 
tion on  January  14,  1913,  and  thereafter 
about  two  days  later  each  year. 

17 


XVII 

THE    LITTLE    PLANETS,    OR   THE    ASTEROIDS 

THE  asteroids,  or  minor  planets,  are 
situated  almost  wholly  in  the  vast  space 
between  Mars  and  Jupiter.  Their  orbits  are 
very  irregular,  both  as  to  shape  and  situa- 
tion; but,  so  far  as  is  known,  only  two  of 
them  pass  beyond  the  orbit  of  Jupiter,  and 
only  one  has  been  discovered  which  at  any 
point  in  its  journey  around  the  sun  comes 
nearer  than  the  orbit  of  Mars. 

The  minor  planets  are  called  by  astrono- 
mers almost  indifferently  asteroids  or  planet- 
oids. "Asteroids"  is  probably  the  name  by 
which  they  are  most  popularly  known. 
But  because  they  are  in  fact  simply  little 
bodies  that  revolve  about  the  sun  as  the 
planets  do,  "planetoids"  seems  to  be  more 
truly  descriptive  of  them,  and  it  is  the  word 
I  have  chosen  to  use  here. 

It  was  early  noted  that,  except  in  one  in- 
stance, the  planets  seemed  to  show  in  their 
244 


THE    LITTLE    PLANETS 

distance  from  the  sun  something  like  a 
mathematical  progression.  Struck  by  this  ap- 
pearance, an  astronomer  named  Bode  worked 
it  out  into  a  formula,  known  ever  since  as 
Bode's  law,  though  the  idea  seems  to  have 
originated  with  another  atronomer.  One 
almost  always  sees  it  mentioned  in  any  work 
dealing  with  this  phase  of  planetary  history, 
and  it  is  especially  interesting  because  of  the 
part  it  played  in  the  discovery  of  the  planet- 
oids .  It  was  as  follows :  Beginning  with  noth- 
ing for  Mercury,  add  three  for  Venus,  twice 
three,  or  six,  for  the  earth,  twelve  for  Mars, 
and  continue  thus  to  double  the  number  for 
each  planet  out  to  and  including  Saturn. 
Then  to  each  one  of  the  numbers  so  obtained 
add  four,  and  the  numbers  resulting  will  very 
nearly  represent  the  relative  distances  of 
the  planets  from  the  sun.  Thus: 


o 

4 

3 
4 

6 

4 

12 

4 

24 

4 

48 
4 

96 

4 

192 
4 

384 
4 

4      7     10      16      28      52     100      196      388 

The  exception  was  that  at  the  fifth  number, 

28,  there  was  no  planet  to  correspond,  and 

Jupiter  was  nearly  twice  as  far  away  from 

Mars  as  it  should  have  been  to  conform  to 

245 


THE    WAYS    OF   THE    PLANETS 

the  law,  thus  leaving  room  for  another  planet 
to  occupy  the  allotted  position  and  fill  out 
this  very  beautiful  progression. 

About  nine  years  after  this  law  was  set 
forth  Uranus  was  discovered  circling  out 
in  space  far  beyond  Saturn,  and  was  found 
to  conform  to  the  law  in  a  most  satisfactory 
manner,  its  distance  being  approximately 
twice  that  of  Saturn.  With  such  close  ac- 
cord between  the  actual  distances  and  the 
prescribed  distances  of  the  planets  from  the 
sun,  and  with  the  one  exception  leaving  al- 
most exactly  the  space  allotted  by  Bode's 
law  for  another  planet,  astronomers  natural- 
ly had  a  very  strong  feeling  that  there  must 
be  another  planet  between  Mars  and  Jupi- 
ter. They  accordingly  set  to  work  to  prove 
this,  if  possible,  and  to  find  what  had  be- 
come of  this  lost  member  of  the  planet 
family,  if  it  ever  existed. 

As  a  result  of  this  work,  on  January  i, 
1801,  the  first  planetoid  was  discovered,  and 
in  rapid  succession  many  like  it  were  found, 
until  now  many  hundreds  are  known  to 
astronomers.  Their  discovery  seemed  at 
first  almost  a  certain  confirmation  of  Bode's 
law,  and  the  fact  that  where  one  large  planet 
should  have  been  found  there  proved  to  be 
246 


THE    LITTLE    PLANETS 

such  a  swarm  of  small  ones  could  be  ac- 
counted for  in  no  other  way  than  to  suppose 
that  something  had  happened  in  the  making 
of  the  planet.  At  any  rate,  the  promulga- 
tion of  Bode's  law  was  the  direct  cause  of  the 
search  for  the  missing  planet  which  led  to 
the  discovery  of  the  planetoids.  And  this  is 
the  only  reason  why  Bode's  law  has  continued 
to  be  mentioned  in  the  history  of  the  planets. 
For  it  was  no  real  law,  it  had  no  scientific 
foundation,  and  its  conformity  to  the  facts 
of  the  relative  distances  of  the  planets  was 
only  one  of  those  very  interesting  and  sin- 
gular coincidences  that  startle  one  for  the 
moment  into  thinking  that  there  is  some 
scientific  significance  in  them.  Another  ex- 
ample of  such  a  coincidence  is  in  the  fact 
that  the  mass  of  any  given  planet  exceeds 
the  total  mass  of  all  the  planets  of  any  less 
mass  than  itself. 

In  less  than  half  a  century  after  the  dis- 
covery of  the  first  planetoid,  Neptune  was 
discovered  at  a  distance  not  at  all  corre- 
sponding to  that  indicated  by  Bode's  law. 
It  was  not  nearly  far  enough  away,  and  yet, 
strangely  enough,  it  was  by  taking  Bode's 
law  into  consideration  that  the  position  was 
indicated  which  finally  led  to  the  discovery 
247 


THE    WAYS    OF    THE    PLANETS 

of  the  planet.  So  while  Bode's  law  has  been 
found  to  be  no  law  at  all,  it  is,  nevertheless, 
entitled  to  some  mention  because  of  its  hav- 
ing thus  stimulated  research  that  has  had 
such  important  results. 

No  really  satisfactory  and  final  explana- 
tion of  the  present  state  of  the  planetoids 
has  ever  been  given.  At  one  time  it  was 
suggested  that  another  planet  had  originally 
existed  in  the  space  between  Mars  and 
Jupiter,  and  through  some  catastrophe  had 
been  shattered  into  the  small  bodies  that 
now  occupy  that  space.  But  this  has  been 
shown  to  be  impossible. 

It  is  now  thought  probable  that  in  the 
original  nebula  the  matter  forming  the 
planetoids  might  have  been  prevented  from 
condensing  into  a  planet  by  the  powerful 
gravitative  influence  of  Jupiter.  This  in- 
fluence, however,  was  not  sufficiently  strong 
to  bring  them  entirely  under  his  control. 
Even  yet  he  pulls  some  of  them  five  or  six 
degrees  out  of  the  path  they  otherwise  would 
take  when  they  venture  within  the  limits 
of  his  domain;  but  he  does  not  capture 
them,  so  they  have  been  left  to  circle  around 
the  sun  as  mere  fragments  of  bodies,  with 
no  force  to  combine  and  make  a  world,  no 
248 


THE    LITTLE    PLANETS 

mass  to  hold  an  atmosphere,  and  with  noth- 
ing to  prevent  them  from  quickly  condensing 
and  from  radiating  all  their  heat  into  space. 
They  are,  in  the  main,  just  cold,  dark,  life- 
less rocks  and  lumps  of  matter  whirling 
through  space  in  a  maze  of  interlacing  orbits, 
some  of  them  almost  as  far  from  the  sun  as 
Jupiter  and  some  almost  as  near  as  Mars — 
one,  indeed,  a  little  nearer  than  Mars  at 
certain  times — but  most  of  them  swarming 
more  thickly  about  half-way  between  Mars 
and  Jupiter,  not  far  from  the  place  that 
Bode's  law  assigned  to  a  planet. 

After  the  first  planetoid  was  discovered  and 
had  been  observed  for  a  few  weeks,  it  was 
lost  and  had  to  be  rediscovered  by  means 
of  mathematical  computation  of  its  orbit. 
Where  this  computation  showed  that  it 
ought  to  be,  there  it  was  found,  on  the  very 
last  day  of  the  same  year,  1801.  Early  the 
next  year  another  body  of  the  same  sort  was 
discovered,  two  years  later  another  was 
found,  and  still  three  years  later  a  fourth 
came  into  view.  These  four  were  the  only 
ones  known  in  this  branch  of  the  solar  family 
for  nearly  forty  years  thereafter. 

In  1845  another  period  of  discovery  com- 
menced, and  has  ever  since  continued,  until 
249 


THE    WAYS    OF    THE    PLANETS 

there  are  now  between  six  and  seven  hun- 
dred of  these  little  bodies  that  have  dis- 
closed their  right  to  be  known  as  members 
of  the  sun's  family.  It  is  probable  that 
there  may  be  still  many  more  of  them,  since 
a  new  one  comes  to  light  every  now  and 
then  on  a  photographic  plate,  and  there  is 
no  indication  of  any  limit  to  the  number  that 
may  thus  appear. 

It  is  likely  that  about  all  have  been  dis- 
covered that  can  be  seen  even  with  a  tele- 
scope, for  a  fairly  systematic  and  thorough 
search  has  been  made  of  the  heavens  for 
this  purpose  during  the  last  half-century. 
This  work  has  resulted  in  a  continually  de- 
creasing number  of  discoveries,  until  this 
method  of  search  has  finally  been  practically 
abandoned.  But  it  not  infrequently  hap- 
pens that  in  photographing  the  stars  a  lit- 
tle trail  of  light  is  discovered  on  the  plate, 
showing  that  some  heavenly  body  with  sen- 
sible motion  has  been  caught  on  it.  And 
this  usually  proves  to  be  a  new  planetoid. 
No  matter  how  long  a  photographic  plate  is 
exposed,  the  fixed  stars  imprint  themselves 
on  it  only  as  points  of  light.  When  the 
impression  is  a  little  streak  of  light  instead 
of  a  dot,  the  object  is  shown  to  be  in  motion, 
250 


THE    LITTLE    PLANETS 

and  is  either  a  planetoid,  a  satellite,  or  a 
comet.  The  fixed  stars  would  make  a  trail 
also  if  the  photographic  apparatus  were  not 
regulated  by  clockwork,  so  as  to  follow  the 
star  in  its  apparent  daily  motion  across  the 
skies.  The  planets  and  other  bodies  in  the 
solar  system  are  sufficiently  near  to  have 
a  sensible  motion  in  addition  to  the  motion 
caused  by  the  rotation  of  the  earth,  which  is 
the  only  motion  we  have  to  take  into  ac- 
count in  dealing  with  the  aspects  of  the 
stars. 

The  first  planetoid  discovered  was  called 
Ceres,  the  next  one  Pallas,  the  third  Juno, 
and  the  fourth  Vesta.  This  pretty  custom 
of  naming  them  after  the  gods  and  goddesses 
of  mythology  was  continued,  with  some 
variations,  until  perhaps  three  hundred  had 
been  so  christened.  But  the  number  of  them 
became  too  prodigious;  and  when  so  many 
began  to  swarm  into  view,  waiting  to  be 
named,  the  utilitarian  method  of  designat- 
ing them  simply  by  numbers  in  the  order 
of  their  discovery  was  adopted.  The  only 
distinguishing  feature  of  so  numbering  them 
is  that  each  number  is  placed  in  a  little 
circle.  Thus  Ceres  is  (D,  Pallas  ©,  and  so 
on.  Those  of  them  that  have  any  special 
251 


THE    WAYS    OF    THE    PLANETS 

claim  to  distinction,  however,  are  still  re- 
ferred to  by  their  own  names,  if  they  have 
any,  in  spite  of  this  most  orderly  attempt  to 
make  them  fit  for  easy  reference  in  a  list. 

There  are  so  many  of  the  planetoids,  and 
they  are  so  minute,  that  even  after  they  have 
been  discovered  they  are  frequently  lost 
again.  Hence  it  is  sometimes  uncertain 
when  they  register  themselves  on  the  photo- 
graphic plates  whether  they  are  really  new 
to  us  or  have  been  known  before.  In  such 
cases  they  are  named  temporarily  after  the 
letters  of  the  alphabet,  and,  when  the  alpha- 
bet is  exhausted,  a  second  letter  is  added. 
Thus  A  to  Z,  then  AB  to  AZ,  BC  to  BZ,  and 
so  on  in  a  sort  of  "round."  Sometimes  these 
combinations  of  letters  become  the  fixed 
designation  of  a  planetoid,  as  a  nickname 
sometimes  clings  to  a  person.  And  thus  it 
happens  that  we  sometimes  read  of  one  in 
particular  of  these  little  bodies  that  is  con- 
spicuous for  the  great  eccentricity  of  its 
orbit,  called  "WD."  The  letters  are  not  its 
initials,  but  its  nickname.  It  really  has  no 
name  other  than  its  number  in  the  list;  but 
it  became  famous  while  it  was  temporarily 
designated  as  "WD,"  and  thus  it  continues 
to  be  called. 

252 


THE    LITTLE    PLANETS 

The  aid  of  a  telescope  is  necessary  in  order 
to  see  the  planetoids,  though  it  is  said  that 
Vesta,  under  very  favorable  conditions, 
sometimes  comes  within  the  limit  of  visi- 
bility. She  is  the  brightest  of  them  all, 
though  not  the  largest,  and  her  brilliancy  is 
the  subject  of  much  interesting  speculation 
among  astronomers,  who  have  not  yet  been 
able  to  account  for  it.  She  seems  from  her 
excessive  brightness  to  be  covered  with 
clouds;  and  yet  it  is  manifestly  impossible 
that  so  small  a  body  could  have  held  an 
atmosphere  throughout  these  long  ages, 
though  clouds  presuppose  an  atmosphere. 
No  doubt,  in  time  this  mystery  of  Vesta's 
brilliancy  will  be  made  plain.  Bright  as 
she  is  in  proportion  to  her  size,  and  even  if 
she  sometimes  can  be  seen,  one  cannot  rea- 
sonably expect  anything  very  brilliant  to 
our  view  from  a  body  not  much  more  than 
a  hundred  miles  in  diameter,  shining  by  re- 
flected light,  nearly  two  hundred  million 
miles  away. 

Ceres,  as  far  as  we  yet  know,  is  the  largest 
of  the  planetoids,  and  may  be  something 
more  than  four  hundred  miles  in  diameter. 
Juno  is  somewhere  near  the  same  size.  Pal- 
las is  about  two  hundred  miles  in  diameter, 
253 


THE    WAYS    OF    THE    PLANETS 

and  Vesta  about  one  hundred  and  eighteen. 
No  doubt,  these  four  were  the  first  to  be  dis- 
covered, because  they  are  the  largest  and 
so  the  easiest  to  be  seen.  At  any  rate,  no 
others  yet  seen  exceed  them  in  size,  and  some 
of  the  more  lately  discovered  are  not  more 
than  fifteen  or  twenty  miles  in  diameter. 
Many  of  those  discovered  by  photography 
are  doubtless  even  smaller  than  these,  and 
are,  perhaps,  mere  meteors  in  size.  The 
combined  mass  of  all  those  discovered  up 
to  this  time  is  far  smaller  than  that  of  any 
of  the  large  planets,  or  even  than  that  of 
our  moon.  Their  mass  cannot,  of  course, 
really  be  measured,  because  they  are  too 
small  to  have  any  perceptible  gravitative 
effect  on  other  bodies,  and  mass  can  only 
be  determined  by  the  influence  of  one  body 
on  another.  But  we  do  know  that  their 
aggregate  mass,  if  it  exceeded  "a  certain 
limit,  would  show  some  disturbing  effect 
on  Mars;  and,  since  it  does  not  do  this,  we 
know  that  all  of  them  taken  together  would 
make  an  extremely  insignificant  body. 

While  the  planetoids  all  revolve  around 

the  sun  in  the  same  manner  and  in  the  same 

direction  as  the  planets  do,  yet  they  are  very 

erratic  in  their  courses,  and  do  not  all  keep 

254 


THE    LITTLE    PLANETS 

within  the  narrow  limits  of  the  zodiac 
through  which — happily  for  our  convenient 
observation — the  larger  bodies  travel.  The 
orbits  of  many  of  them  are  extremely  ellipti- 
cal, while  some  are  almost  circles;  and  their 
inclination  to  the  ecliptic  varies  from  al- 
most nothing  to  nearly  fifty  degrees.  If  one 
could  catch  from  one  side  a  view  of  them  all 
together,  they  would  have  much  the  appear- 
ance in  space  of  a  flock  of  swallows,  the  indi- 
viduals darting  this  way  and  that,  passing 
above  and  below  one  another  in  such  intri- 
cate sweeps  and  sinuosities  that  it  would  be 
impossible  to  keep  track  of  them  separate- 
ly. And  yet  time  has  brought  these  ap- 
parently tangled  orbits  into  such  nice  ad- 
justment that  the  little  bodies  can  continue 
to  cross  and  recross  each  other's  paths  with 
no  danger  of  interference  from  each  other. 
Such  collisions  as  there  may  have  been 
occurred  in  the  very  beginning  of  their 
careers.  Such  of  them  as  came  into  col- 
lision then  traveled  on  together  as  one  body 
until  accommodation  was  made  for  all. 

One  of  the  most  wide-wandering  of  these 

tiny  bodies  has  been  named  Eros,  after  the 

little  god  of  love,  more  commonly  known 

as  Cupid.     It  has  a  particular  interest  for 

255 


THE    WAYS    OF    THE    PLANETS 

us,  because  of  all  the  heavenly  bodies  it  at 
times  comes  nearer  to  us  than  any  except 
the  moon  and  an  occasional  comet.  At  its 
nearest  it  is  within  fourteen  million  miles 
of  the  earth,  which  is  more  than  ten  million 
miles  nearer  than  the  closest  approach  of 
Venus,  the  nearest  of  the  large  planets. 

This  little  body  was  thus  near  us  in  1894; 
but  we  did  not  then  know  this,  for  Eros  was 
not  discovered  until  1898.  After  its  dis- 
covery, however,  it  was  traced  back  on 
many  photographic  plates,  and  the  fact  that 
it  had  been  in  our  neighborhood  was  learned. 
For  untold  ages  it  has  been  making  these 
visits  to  us  every  thirty-seven  years,  and  we 
have  known  nothing  of  them.  Its  next  near 
approach  will  be  in  1931,  and  it  will  continue 
to  come  thereafter  every  thirty-seven  years. 
Now  that  we  know  about  them,  these  visits 
are  not  only  pleasant  to  contemplate,  but 
it  is  expected  that  when  they  occur  the 
planetoid  will  be  of  great  scientific  value  to 
us  in  helping  to  determine  more  surely  and 
accurately  the  exact  distance  of  the  sun. 

The  planetoids,  though  so  minute  and  of 
no  value  as  a  spectacle,  have  been,  and  still 
are,  very  useful  little  bodies  to  us  in  a  scien- 
tific way.  In  addition  to  furnishing  an  easy 
256 


THE    LITTLE    PLANETS 

means  of  measuring  the  distance  of  the  sun, 
they  promise  to  throw  some  light  on  various 
questions  of  physics  in  which  the  planets, 
too,  are  involved.  The  brilliancy  of  Vesta, 
for  instance,  which  has  been  mentioned,  and 
the  unaccountable  variability  in  the  bright- 
ness of  some  others  of  them  have  yet  to  be 
adjusted  to  known  physical  laws.  Even  the 
extreme  eccentricity  of  some  of  their  orbits, 
and  the  large  tilt  of  some  of  them  to  the 
ecliptic,  may  be  suggestive  in  finally  solv- 
ing certain  planetary  problems,  for  these 
impish  little  bodies  are  far  from  conforming 
to  the  regular  ways  of  the  planets,  and  there 
is,  of  course,  some  mechanical  reason  for 
their  apparent  waywardness. 


XVIII 

CONCLUSION 

THE  great  variety  of  beauty  that  the 
planets  present  to  us  is  sufficient  to 
keep  us  always  interested  in  them,  when 
once  we  have  acquired  an  acquaintance  with 
them.  Rarely  is  there  an  evening  when 
some  one  of  them  does  not  enhance  the  charm 
of  the  splendid  spectacle  of  the  sky  in  which 
all  the  heavenly  bodies  save  the  sun  have  a 
part.  Their  greater  brilliancy  often  brings 
them  into  view  before  the  stars  have  begun 
to  glow  in  the  evening,  and  prolongs  our 
sight  of  them  after  the  rays  of  the  sun  have 
blotted  out  the  light  of  the  stars  in  the 
morning.  Thus  they  are  always  single  in 
their  loveliness,  and  always  hold  a  dis- 
tinguished place  in  the  midst  of  the  brilliant 
company  of  the  stars. 

Having  considered  these  brilliant  bodies 
individually  and  in  detail,  as  we  have,  we 
ought  by  this  time  to  be  able  to  identify 
258 


CONCLUSION 

any  one  of  them  that  shows  itself  in  the 
evening  sky,  and  to  have  a  pretty  fair  notion 
of  the  general  character  and  peculiarities  of 
each.  But  even  if  one  does  not  much  care  for 
detailed  information  concerning  them,  or, 
before  seeking  that,  prefers  first  to  become 
familiar  with  their  appearance,  a  quick  and 
sure  recognition  of  them  may  be  had  by 
noting  their  positions  and  their  very  strik- 
ing individual  aspects  as  set  forth  in  the 
preceding  chapters. 

On  seeing  a  bright  object  in  the  sky  that 
does  not  seem  to  be  a  familiar  star,  simply 
stop  and  look  at  it.  Does  it  twinkle?  If 
it  does  not,  it  is  a  planet.  If  it  is  more  than 
forty-five  degrees  from  the  sun,  or  if  it  is 
seen  at  a  time  when  the  sun  has  been  down 
more  than  three  hours,  then  it  is  neither 
Mercury  nor  Venus,  and  must  be  either 
Mars,  Jupiter,  or  Saturn.  Is  it  very  bright 
and  pinkish  in  tone?  Then  it  is  Jupiter. 
Is  it  very  bright  and  quite  red?  It  is  Mars, 
not  far  from  opposition.  Is  it  not  very 
bright,  but  small  and  rosy?  Then  it  is 
Mars  going  toward  conjunction.  Is  it  yel- 
low in  tone  and,  while  large  and  conspicuous, 
still  not  so  very  brilliant?  It  is  Saturn. 

If  the  planet  we  seek  to  name  is  nearer  to 
18  259 


THE    WAYS    OF    THE    PLANETS 

the  sun  than  forty-five  degrees,  but  is  still  well 
above  the  horizon,  it  may  be  either  of  these 
three — Mars,  Jupiter,  Saturn — or  it  is  Venus. 
If  it  is  very  bright  and  silvery,  it  is  certainly 
Venus.  If  it  is  very  low  in  the  sky  and  very 
near  the  sun,  it  may  be  any  one  of  the  five 
visible  planets.  In  such  a  position  Mars 
will  always  be  very  small,  and  the  others 
always  larger  than  a  first-magnitude  star; 
and  they  may  all  twinkle  a  little — Mercury 
almost  as  much  as  a  star.  Their  size  will 
show  them  all  (except  Mars)  as  planets,  but 
it  will  be  somewhat  more  difficult  to  tell 
which  is  which  than  it  is  when  they  are 
higher  up  in  the  sky.  The  best  thing  to  do 
in  such  circumstances  is  to  look  up  their 
positions  either  in  this  book  or  in  an  almanac. 
The  almanac  will  serve  as  a  footman  to 
announce  them.  The  book,  it  is  hoped,  has 
so  recorded  their  peculiarities  and  habits 
that  either  their  appearance  or  their  place 
will  be  sufficient  to  make  them  known. 

In  any  event,  the  problem  of  identifica- 
tion in  this  position  will  not  keep  one  long, 
for  in  a  situation  presenting  these  greater 
difficulties  the  planet  will  be  visible  for  less 
than  an  hour  after  sundown.  Besides,  it 
is  not  likely  at  such  times  to  attract  one's 
260 


CONCLUSION 

involuntary  attention,  but  when  under  ob- 
servation in  such  a  situation  is  usually  sought 
out  by  those  already  somewhat  informed  as 
to  the  planet's  habits  and  appearance,  which 
will  betray  its  identity.  It  is  information 
of  this  sort  that  I  have  endeavored  to  give 
in  these  pages,  and  it  is  hoped  that  the 
reading  of  them  will  be  the  beginning  of  a 
long  and  intimate  acquaintance  with  these 
charming  and  always  interesting  individ- 
uals. 

Individuals  the  planets  inevitably  become 
to  any  one  who  learns  to  know  them  during 
the  long,  quiet  nights  in  the  country,  or 
wherever  an  opportunity  is  afforded  really 
to  contemplate  their  peculiar  traits  and  fea- 
tures. Like  individuals  of  whatever  kind, 
they  impress  different  persons  in  different 
ways.  As  I  have  watched  them  from  year 
to  year  I  have  come  to  have  a  very  distinct 
impression  of  Jupiter  as  slow  and  majestic, 
and  yet  not  lacking  in  joviality;  Saturn  as 
friendly,  but  reserved;  Mars  as  sturdily 
brisk  and  busy;  Venus  as  always  gracious 
and  smiling;  and  Mercury  as  irresponsible 
and  roguish.  Others  might  have  an  entirely 
different  feeling  in  regard  to  them;  but  an 
intimate  acquaintance  with  them,  which  is 
261 


THE    WAYS    OF    THE    PLANETS 

not  wholly  scientific,  cannot  fail  to  stamp 
them  as  in  some  sort  individuals. 

And  when  we  consider  that  these  interest- 
ing individuals  are  closely  related  members 
of  our  cosmic  family,  their  ever  -  changing 
beauty  of  aspect,  the  history  of  their  de- 
velopment and  their  affairs  generally,  gain 
a  significance  to  us  that  no  other  heavenly 
bodies  can  have.  The  two  groups  of  planets 
— the  inner  and  the  outer — are  like  two  sets 
of  children  in  a  family:  born  of  the  same 
parent,  but  under  very  different  circum- 
stances, and  in  very  different  surroundings. 
Mars,  the  earth,  Venus,  and  Mercury  are  all, 
as  compared  with  the  outer  planets,  small 
and  dense,  with  more  or  less  thin  atmos- 
pheres and  an  abundance  of  heat  and  light. 
They  all  lie  comparatively  near  to  the  sun, 
and  are  composed  of  the  denser  material 
lying  near  the  center  of  the  great  nebula, 
which  was  the  original  form  of  the  entire 
solar  system.  Probably  denser  to  begin 
with  than  the  others,  they  have,  on  account 
of  their  diminutive  size,  developed  more 
rapidly  and  are  further  advanced  toward 
the  final  state  of  solidity  which  we  shall 
all  attain  in  the  end.  Mercury,  the  smallest, 
is  already  old  and  seamed  and  hardened. 
262 


CONCLUSION 

Mars,  the  next  in  size,  is  well  advanced,  but 
still  has  an  atmosphere  and  some  other  signs 
of  vitality.  Venus,  though  we  know  so  lit- 
tle about  her,  has  probably  a  long  period 
of  development  yet  before  her;  while  this 
warm,  nourishing  earth,  which  seems  to  us 
the  best  one  of  them  all,  will  probably  for 
a  still  longer  time  than  Venus  hold  its 
atmosphere  and  remain  green  and  flour- 
ishing. 

On  the  other  side  of  the  vast  space  which 
divides  the  two  groups  of  the  sun's  family 
dwell  Jupiter,  Saturn,  Uranus,  and  Neptune. 
They  are  all  tremendous  in  volume,  en- 
veloped in  immense  atmospheres,  far,  far 
from  our  common  source  of  heat  and  light, 
of  comparatively  slight  density,  and  prob- 
ably formed  from  the  lighter  material  com- 
posing the  outer  edges  of  the  parent  nebula, 
and,  because  of  their  immense  size,  still  in 
a  very  early  stage  of  development.  The 
two  groups  could  scarcely  seem  more  widely 
different  if  they  belonged  to  different  systems ; 
but  the  members  of  each  are  all  closely  akin, 
and  each  one  in  its  own  way,  determined  by 
its  size  and  environment,  is  developing  tow- 
ard the  same  end. 

If  there  is  life  on  any  of  these  outer 
263 


THE    WAYS    OF    THE    PLANETS 

planets,  it  must  be  of  a  sort  of  which  we 
have  no  conception.  Jupiter  and  Saturn 
are  probably  red-hot,  and  could  sustain 
nothing  more  cold-blooded  than  a  race  of 
salamanders,  though  why  a  race  of  intelli- 
gent salamanders  should  or  should  not  exist 
there,  is  a  question  that  one  might  make  bold 
to  answer  according  to  one's  fancy.  Uranus 
and  Neptune  are  smaller,  and  perhaps  less 
hot  than  Jupiter  and  Saturn;  but  we  really 
know  very  little  about  the  state  of  their 
domestic  affairs,  and  the  little  we  do  know 
in  no  way  indicates  a  place  of  abode  for  any 
sort  of  intelligence  conceivable  to  us.  We 
can,  however,  conceive  of  a  time  in  the  far- 
distant  ages  when  these  four  hot  and  vapor- 
ous planets  may  have  become  sufficiently 
condensed  to  have  a  solid  crust,  and  yet  have 
sufficient  internal  heat  to  moderate  the  frigid 
temperature  that  would  be  normal  at  their 
distance  from  the  sun,  and  they  might 
then  support  life  even  somewhat  resembling 
and  perhaps  even  more  gloriously  beauti- 
ful than  that  with  which  we  are  famil- 
iar. 

Of  the  existence  of  life  somewhat  similar 
to  ours  on  the  smaller,  near-by  planets  we 
may  have  something  nearer  a  reasonable  con- 
264 


CONCLUSION 

ception,  though  we  are  nowhere  near  the 
possession  of  any  real  knowledge  concerning 
it.  Mercury,  we  have  every  reason  to  think, 
cannot  support  life,  mainly  because  of  his 
lack  of  atmosphere;  but  also  because  of  his 
long  rotation,  which  affords  no  alternations 
of  day  and  night,  but  leaves  him  with  one 
side  always  burning-hot  and  the  other  in- 
conceivably cold.  Venus  might  very  well 
have  a  climate  not  utterly  unlike  ours,  and 
hence  be  habitable  for  beings  somewhat  re- 
sembling us,  if  she  has,  as  she  has  long  been 
thought  to  have,  a  heavier  atmosphere  than 
the  earth  has,  and  if  she  has  alternations  of 
day  and  night.  But  we  have  seen  that,  owing 
to  the  obscurity  of  the  surface  of  Venus,  our 
knowledge  in  regard  to  these  conditions  is 
far  from  certain,  and  we  have  little  reason 
to  have  even  speculative  ideas  concerning 
life  there.  With  Mars  it  is  a  more  open 
question.  We  can  see  that  planet,  and  see 
it  fairly  well.  It  has  an  atmosphere  and 
changes  of  seasons,  and  while  it  may  not 
afford  a  climate  that  would  be  exactly  attrac- 
tive to  us  as  a  place  of  transmigration,  it 
is  not  particularly  unreasonable  to  let  our 
fancy  play  over  the  rather  pleasant  specula- 
tion concerning  the  presence  there  of  beings 
265 


THE    WAYS    OF    THE    PLANETS 

at  least  understandable  by  us,  even  if  not 
wholly  congenial. 

Whatever  each  planet  affords  in  the  way 
of  life  and  human  interests,  all  of  them  must 
ever  be  to  us  the  most  interesting  things  in 
all  nature,  outside  of  our  own  earth,  in  the 
two  regards  already  pointed  out:  first,  as 
the  most  beautiful  objects  of  vision  among 
all  the  starry  hosts,  and,  second,  as  our  near- 
est kindred  in  this  universe  of  suns  and 
systems  of  worlds.  Together  the  earth  and 
they  circle  ceaselessly  around  and  around 
the  sun,  following  in  nicely  adjusted  orbits 
that  great  luminary  as  it  sweeps  majestically 
on  through  space  toward  the  beautiful  Vega, 
itself  a  sun,  and,  so  far  as  we  now  know,  in 
this  close  companionship  we  shall  continue 
until  every  planet  and  the  sun  itself  has  be- 
come cold  and  dark  and  lifeless.  And  then, 
perhaps,  or  even  before  the  light  of  our 
system  is  finally  extinguished,  we  may  meet 
another  wandering  sun,  and  in  the  mar- 
riage of  the  two  great  bodies  another  system 
of  worlds  may  be  evolved  of  which  we  and 
the  planets  shall  form  a  part. 


SYMBOLS  USED  IN  ALMANACS 

£  =  Mercury.  •=rNew  Moon. 

$  =  VenuS.  »=  First  Quarter. 

©  —  Full  Moon. 
©  =  Earth.  <[  =  Last  Quarter. 


c5  =  Con  junction    with    the 

If  =  Jupiter.  sun  ;  or,  in  the  case 

of  two  planets  or  a 
T>  =  Saturn.  planet  and  the  moon, 

near  together. 
]£   or  $  =  Uranus. 

5>  =  Opposition. 

tj;  =  Neptune.  Q  :=  Quadrature. 

Examples  : 

<5  ^  5  =  Mars'  and  Venus  near  together. 

5>  y  Q  =  Jupiter  in  opposition. 

(3  y  O  —  Jupiter  in  conjunction. 

c5  $  Q  Inf.  =  Mercury  in  inferior  conjunction. 

c5  $  O  SUP-  =  Mercury  in  superior  conjunction. 

(5$])  =  Venus  and  Moon  near  together. 


INDEX 


ADAMS,  236^238. 

Alcor,  star  in  Great  Dipper, 

105,  236. 
Aldebaran,    first-magnitude 

star,  79-80,  153,  1 88,  210. 
Antares,  star  in  Scorpio,  86, 

153,   160,    187,   189,  209, 

212. 

Aquarius,  constellation  of 
the  zodiac,  76,  88-89,  91" 
92,  187,  212-213,  22I»  242- 

Arcturus,  24,  84;    color  of, 

IO2. 

Ariel,    satellite    of    Uranus, 

232-233. 
Aries,    constellation   of    the 

zodiac,  76-78,  90-92,  212, 

242. 
Asteroids,  244-257. 

BEE-HIVE,  82,  211-212. 
Bode's  law,  245-249. 
Bootes,  star  of  first  magni- 
tude, 102. 

CALLISTO,  satellite  of  Jupi- 
ter, 200,  205. 

Cancer,  constellation  of  zo- 
diac, 76,  82,  91-92,  188, 

2II-2I2. 

Capella,  star  of  first  magni- 
tude, 191. 


Capricornus,  one  of  the 
twelve  constellations  of 
the  zodiac,  76,  88-89,  91" 
92,  187,  212,  229. 

Cassiopeia,  constellation,  77. 

Castor  and  Pollux,  81,  188, 
211,  242-243. 

Ceres,  first  planetoid  dis- 
covered, 251,  253. 

Constellations  of  the  zodiac, 
75-92- 

DEIMOS,   satellite  of  Mars, 

180-181. 
Dione,    satellite  of   Saturn, 

222. 

EARTH,  relation  to  planets, 
11-15,  r95  nearness  to 
sun,  19;  terrestrial  planet, 
41;  movement  of,  51;  po- 
sition in  regard  to  Mer- 
cury, 1 20-121;  likeness  to 
Venus,  138-140. 

Enceladus,  satellite  of  Sat- 
urn, 222. 

Encke's  comet,  109. 

Equinox,  derivation  of  word, 

74- 

Eros,  small  planet,  255-256. 
Europa,  satellite  of  Jupiter, 
200-20 i. 


269 


THE    WAYS    OF    THE    PLANETS 


FLAGSTAFF,  Arizona,  obser- 
vatory of,  175-176. 
Fomalhaut,  187,  209,  213. 

GALILEO,  136. 
Ganymede,  satellite  of  Jupi- 
ter, 2OO-2OI,  2O5. 

Gemini,  constellation  of  the 

zodiac,  76,  81-82,  91-92, 

188,  210-211,  213. 
George    III.,    Uranus    first 

called     Georgium     Sidus 

after,  226. 
Great  Dipper,  73,  77,  84,  96, 

104,  105,  186,  236. 

HAMAL,  star  in  constellation 
of  Aries,  78. 

Herschel,  ^discovery  of  Ura- 
nus by,'  226-227,  232. 

Hyades,  the,  79. 

Hyperion,  satellite  of  Saturn, 
222. 

INFERIOR  planets,  40. 
lo,  satellite  of  Jupiter,  200, 
201. 

JAPETUS,  satellite  of  Saturn, 

222. 

Juno,  planetoid,  251,  253. 

Jupiter,  color,  5;  attraction 
between  Saturn  and,  15; 
distance  from  sun,  19; 
size  and  importance  of, 
20;  movement,  25,  65; 
satellites,  34,  106,  199- 
205;  long  known,  38;  su- 
perior planet,  41;  space 
between  Mars  and,  42; 
influence  on  comets,  44; 
gibbous,  66 ;  distance  from 
ecliptic,  72 ;  near  Antares, 


86;  in  Scorpio,  127;  size 
and  velocity,  183-185; 
place  in  sky,  186-190; 
distance,  light,  and  heat, 
190-193;  seasons  and  at- 
mosphere, 193-195;  sur- 
face features,  195-199; 
symbol,  205;  compared 
to  Saturn,  213-214,  215- 
218;  nearness  of  asteroids 
to,  244;  how  to  recognize, 
259-264. 

LAPLACE,  nebulae  hypothesis 

of,  28,  30. 
Leo,  constellation  of  zodiac, 

76,  82-83, 9I~92»  I88»  2II~ 

212,  221. 

Leverrier,  discovery  of  Nep- 
tune by,  236-238. 

Libra,  constellation  of  zo- 
diac, 76,  85,  91-92,  188, 

212. 

Little  Dipper  of  the  Pleiades, 

79- 
Lyre,    constellation   of   the, 

54- 

MAJOR  planets,  19. 

Mars,  "eye"  of,  12;  dis- 
tance from  sun,  19;  near- 
ness to  earth,  20;  move- 
ment of,  25,  65;  long 
known,  38 ;  superior  plan- 
et, 41;  space  between 
Jupiter  and,  42;  speed, 
51;  gibbous,  66;  distance 
from  ecliptic,  72;  color, 
80,  86,  259;  position  in  re- 
gard to  Antares,  87;  den- 
sity, no;  nearness  to 
Venus,  128;  variety  in 


270 


INDEX 


brightness,  151-152;  how 
and  where  to  identify, 
152-162,  259-265;  size, 
atmosphere,  and  tempera- 
ture, 162-165;  distance 
and  brilliancy,  166-170; 
seasons,  170-171;  surface 
aspect,  172-179;  satel- 
lites, 180-181;  symbol  of, 
182;  nearness  of  asteroids 
to,  244;  Bode's  law  and, 
245-246,  248-249;  small- 
ness,  260. 

Mercury,  18;  nearest  planet, 
19;  unfavorable  situation 
for  observation,  20;  easily 
recognized,  22;  age  of,  34; 
dense  matter  of,  37;  long 
known,  38;  inferior  planet, 
40;  terrestrial  planet,  41; 
irregularities  of,  44-45 ; 
number  of  revolutions,  47; 
orbit,  48;  apparent  mo- 
tions, 57-58;  transits,  61; 
distance  from  ecliptic,  72- 
73;  color,  80,  86;  in 
Scorpio,  87;  elusiveness 
of,  93-95 ; ,  how  to  find,  96- 
100,  259;  distance  and 
brightness  of,  101-105; 
size,  106-110;  relation  to 
sun,  1 11-118;  transits, 
119-121;  lack  of  atmos- 
phere, 144,  146;  resem- 
blance to  Mars,  153; 
Bode's  law  and,  245. 

Milky  Way,  87,  88,  89. 

Mimas,  satellite  of  Saturn, 
222. 

Minor  planets,  19. 

Mizar,  star  in  Great  Dipper, 
105,  236. 

Moon,     23;      once     called 


planet,  39;   distance  from 
ecliptic,  73. 
Moulton,  Professor,  178. 

NEPTUNE,  discovery,  15;  dis- 
tance from  sun,  19,  43; 
not  visible  to  naked  eye, 
20;  age,  34;  diffuse  mat- 
ter of,  37;  unknown  to 
ancients,  40;  superior 
planet,  41;  influence  on 
comets,  44;  one  revolu- 
tion, 47 ;  orbit,  48 ;  move- 
ment of,  65;  distance 
from  earth,  234;  discov- 
ery, 235-237,  247;  sym- 
bol, 238;  atmosphere,  239— 
240;  satellite,  241;  mo- 
tion, 242;  brightness,  243. 

OBERON,  satellite  of  Uranus, 

232-233. 
Orion,  123. 

PALLAS,  planetoid,  251. 

Phecda,  star  in  Great  Dip- 
per, 104. 

Phobos,  satellite  of  Mars, 
180-181,  202. 

Phoebe,  satellite  of  Saturn, 
222-223. 

Pisces,  constellation  in  zo- 
diac, 76-77,  90-92,  160, 

187,  212,  242. 

Pleiades,    79~8o,    153,    188, 

210. 

Praesepe,  or  the  Bee-hive,  82, 

2II-2I2. 

REGULUS,  star  in  the  con- 
stellation of  Leo,  83-84, 

188,  212. 


271 


THE    WAYS    OF  THE    PLANETS 


Rhea,  satellite  of  Saturn, 
222-223. 

SAGITTARIUS,  constellation 
of  zodiac,  76,  87-88,  91- 
92, 186, 189,  209,  212,  229. 

Saturn,  rings  and  moons 
of,  12,  218-223;  distance 
from  sun,  13,  19;  attrac- 
tion between  Jupiter  and, 
15,  185;  size  and  impor- 
tance, 20;  object-lesson 
from,  29;  long  known,  38; 
superior  and  outer  planet, 
41-42;  influence  on  com- 
ets, 44;  length  of  year  on, 
47;  movement,  65;  dis- 
tance from  ecliptic,  72; 
satellites,  106;  color,  206, 
209,  259;  as  evening  star, 
207;  slight  motion,  208; 
circuit  of  skies,  209-213; 
size  and  distance,  213- 
215;  surface  aspects,  215- 
216;  day  and  night,  217- 
218;  seasons,  224;  sym- 
bol, 224;  Bode's  law  and, 
245-246;  how  to  recog- 
nize, 260-264. 

Schiaparelli,  174-175. 

Scorpio,  constellation  of  zo- 
diac, 76,  85-88,  91-92, 
127,  153,  186,  188,  212- 
213. 

Sidereal  year,  49-50. 

Sirius,  the  dog-star,  123. 

Spica,  84-85,  1 88. 

Sun,  controls  planets,  14,  17; 
distance  from  earth,  18; 
center  of  planet  system, 
27;  probable  formation  of , 
36;  once  called  planet, 
39;  situation  in  orbit,  52; 


vernal  equinox,  76;  rela- 
tion to  Mercury,  in-n8; 
relation  to  Mars,  166-167; 
relation  to  Jupiter,  183- 
185. 

Superior  planets,  41,  65-70. 

Symbols  in  almanacs,  267. 

Synodic  year,  50,  52. 

TAURUS,  constellation  in  zo- 
diac, 76,  79-8ot  90-92, 

188,  210,  212,  242. 

Tethys,  satellite  of  Saturn, 

222. 
Themis,  satellite  of  Saturn, 

222-223. 
Titan,    satellite   of    Saturn, 

222-223. 
Titania,  satellite  of  Uranus, 

232. 
Triangulum,  78. 

UMBRIEL,  satellite  of  Uranus, 
232-233. 

Uranus,  gravitational  influ- 
ence on,  15;  distance  from 
sun,  19,  229-230;  un- 
known to  ancients,  40; 
superior  planet,  41;  in- 
fluence on  Neptune,  43; 
influence  on  comets,  44; 
movement,  65;  nearness 
to  ecliptic,  72;  discovery, 
225-226,  246;  symbol, 
227;  time  of  revolution, 
228;  size,  231;  satellites, 
232-233;  irregularity  of, 
236. 

VEGA,  in  constellation  of  the 

Lyre,  54,  191,  266. 
Venus,  the  planet,  2,  4,  5; 

nearness  to  sun,  19;  near- 


272 


INDEX 


ness  to  earth,  20,  256; 
movement  of,  25;  long 
known,  38;  early  names 
of,  39;  inferior  planet, 
40;  terrestrial  planet,  41; 
brightest  planet,  42;  ap- 
parent motions,  57-58 ; 
transits,  61 ;  distance  from 
ecliptic,  72;  seen  from 
Mercury,  105;  density, 
no;  beauty,  122;  how 
and  when  to  see,  123- 
131;  distance  and  bright- 


ness, 132-137;  likeness  to 
earth,  138-140;  atmos- 
phere and  seasons,  141— 
147;  transits,  147-149; 
sign  of,  150;  Bode's  law 
and,  245;  how  to  know, 
259-264. 

Vesta,  planetoid,  251,  253, 
.254,  257. 

Virgo,  constellation  of  the  zo- 
diac, 76,  84-85,  1 88,  212. 

ZODIAC,  the,  71-92. 


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